2. Platitudes about backing

Separatism is the view that explanations are separate from the facts that make them obtain. In this sense, separatism is a minimal thesis (although some of its versions might be more plausible than others).Footnote ⁶ Still, since the focus of this paper is the backing relation that obtains between these two separated entities, I will bring up plausible features of separatism that are relevant to my discussion when appropriate.

In this section, I will propose a functional definition of backing based on minimal assumptions about its nature. Then, I will clarify and motivate these features, thus showing that they can act as prior constraints for any proposed theory of backing. The functional characterization I want to propose is the following:

A couple of specifications are in order. First, the nontriviality clause makes sure that relations such as ‘being in the same world as’ do not come out as backing relations. Secondly, the success conditions of an explanation are those conditions that, once they are met, necessitate that the explanation is successful. When a grounding-fact backs an explanation, then that fact contributes to the satisfaction of the success conditions of that explanation.Footnote ⁷ Thirdly, this characterization involves grounding-facts but there is no reason to think that it cannot be extended to other kinds of facts as well.Footnote ⁸ I begin my discussion by focusing on grounding since backing has received attention primarily in the context of grounding (Raven Reference Raven2015; Schaffer Reference Schaffer2016). Even though, as mentioned, the backing-locution can also be found in other domains, it is fair to expect that the main source of my audience are people interested in grounding.Footnote ⁹ Finally, I take backing to be cross-categorical in the sense that backers (in this case, grounding-facts) are different in kind from the explanations they back. This is perhaps the most contentious proposed feature of backing and for this reason it requires further discussion.

Why think that backing is cross-categorical? First, I take cross-categoricity to be a default feature of backing. Taking at face value the way the term backing is used in the literature entails that backing is cross-categorical. Grounding-facts are taken to be worldly and broadly stance independent, whereas explanations are about such facts (thus, representational in character). This is particularly salient if one considers the relation between causal events and the explanations which they back. As Schaffer (Reference Schaffer2016, 36) puts it:

Secondly, it is independently plausible that explanations are ontologically different from their backers. Consider causation again. Causal explanations are apt to pragmatic/epistemic constraints whereas the causal relation itself typically is not.Footnote ¹⁰ To compare, separatists about grounding make analogous remarks (Sjölin Wirling Reference Sjölin Wirling2020, 2–3). In this sense, it is no accident that separatists about grounding model their view according to the relation between causation and causal explanation.

There are ways to resist the cross-categoricity of backing. Sjölin Wirling (Reference Sjölin Wirling2020, 4, 5, 6), in an interesting move, argues that explanations are not the proper kind of relatum for the backing relation. Rather, she argues, a grounding-fact like [A grounds B] backs the fact that ‘A explains B’ is an explanation. In other words, backers back the explanatoriness of that which represents them. In this sense, backing is not cross-categorical since both of its relata are facts.

It could be argued that one can translate explanation-talk into fact-talk: saying ‘a grounding-fact G backs an explanation E’ can be translated into ‘G backs the fact that E is an explanation.’ But it is unclear if one should do so. First, translating talk of one ontological category to another does not come for free. To compare, consider operator-based views of grounding being translated into relational-talk. This is certainly possible, but one would need to make some substantive ontological assumptions along the way (i.e., countenancing a relation of grounding). In this sense, it is unclear if the results of such translation procedures can be trusted. More importantly, it seems to me that the explanation ‘A explains B’ and the fact that ‘A explains B’ is an explanation are importantly different entities. The former is an explanation, whereas the latter is a fact about that explanation. To my mind, backing concerns the former.

Identifying the facts that determine the fact that ‘A explains B’ is an explanation is an interesting (albeit different) question. There are two versions of this question. The first reading concerns the fact that ‘A explains B’ is a successful explanation (Sjölin Wirling [Reference Sjölin Wirling2020, 4] seems to adopt this reading). But this fact is not “backed” in the original sense. Rather, it holds in virtue of the fact that ‘A explains B’ is fully backed (in the sense that its success conditions are fully met). The second reading concerns the fact that ‘A explains B’ is an explanation (successful or not). I cannot settle this question here, but I am inclined to think that facts about the explanatoriness of a putative explanation are grounded in certain of its structural features. For example, on Kim’s proposal (Reference Kim1994), explanations are propositions that have three “slots”: one for the explanans (or explanantia), one for the explanandum, and one for the determination-relation that connects the underlying phenomena (more on this later). At any rate, I take the question concerning the nature of the relations that are involved in these two readings to be an open question (and distinct from the issue concerning the nature of backing).

Finally, it could be argued that even if Sjölin Wirling is wrong about the exact details of the explanation-relatum, backing is still monocategorical in the following sense (bracketing translatability worries): backing could be the relation between the fact that A grounds B and the fact that A explains B. Footnote ¹¹

I have the following response. The cross-categoricity of backing should be understood in a general, nonfetishistic, way. A relation is cross-categorical when it relates entities that are importantly different from one another, even if those entities belong (strictly speaking) to the same ontological category. As noted, grounding relations are worldly items whereas explanations are representational entities about those items. In this sense, even if explanations are facts, the kinds of facts that they are differ significantly from the kinds of facts that grounding-facts are.Footnote ¹²

3. Backing as explaining

So, what would the relation between an explanation and its backer be? The first proposal I will examine has been advanced by Kovacs (Reference Kovacs2017, 2934; Reference Kovacs2019a, 6) who identifies “backing” with “explaining”:

For example, according to (B=E), an explanation of a specific mental state in virtue of a brain state is explained by the fact that the latter grounds the former.

I have two worries against this proposal. The first worry concerns the cross-categoricity of backing. As mentioned, the grounding separatist view does not simply claim that explanations are distinct from their corresponding grounding-facts. Specifically, the claim is that explanations are separate from grounding-facts and different in kind. But (B=E) cannot accommodate this datum. I take it that the explanation-relation obtains between the explanandum and the relevant explanans (or explanantia). In this sense, every theory of explanation takes explanations to relate the same kind of entities. As mentioned, some views take explanations to be arguments: explanantia and explananda are both propositions or sets of sentences (Kitcher Reference Kitcher, Kitcher and Salmon1989). Others take the explanation-relation to be a connective: explanantia and explananda are nonreified, linguistic, entities (Schnieder Reference Schnieder2010).Footnote ¹⁶ Or, perhaps, explanations are relations between worldly items as per the so-called ontic conception of explanation.Footnote ¹⁷ No theory of explanation, which I know of, takes (or can take) the explanation-relation to be cross-categorical.Footnote ¹⁸

My second worry against (B=E) appeals to a particular version of the separatist view. If the separatist view is that every successful explanation is backed, and if to be backed is to be explained, then we get the following thesis:

But (Explanation Maximalism) leads to a regress since it requires the existence of an infinite series of explanations.

The proponent of (B=E) might respond by saying that the resulting regress is benign. But this move does not come cheap. First, it is not that clear what counts as a vicious regress. Some believe that vicious regresses are regresses that have some specific structural feature. Others disagree and take viciousness to be context relative. So, it seems that in order for the proponent of (B=E) to claim that the relevant regress is benign, additional (and controversial) assumptions about the nature of regresses must be made.Footnote ¹⁹ Secondly, even if we accept that (Explanation Maximalism) leads to a benign regress, it is still the case that (B=E) has to countenance a regress. And even benign regresses have implications for one’s ontology. Specifically, (Explanation Maximalism) leads to the existence of infinite explanations. This is still a cost for (B=E).Footnote ²⁰

The obvious move for the proponent of (B=E) would be to reject (Explanation Maximalism) and claim that only some successful explanations are explained. Such a view is entailed by the weaker separatist view that only some successful explanations are backed. This move avoids the regress worry. It does so, however, at a significant cost. Again, more questions are raised. Which explanations are not backed? And (once we identify them), why is it the case that these explanations are as such that they do not require a backer? Again, I take these questions to not have obvious or easy answers.Footnote ²¹

Finally, and perhaps more importantly, accepting that only some explanations are explained requires the existence of successful but unbacked (or bare) explanations (bare explanations, henceforth). Bareness should be distinguished from fundamentality. An explanation can be fundamental but still backed in the sense that it holds in virtue of a fundamental fact. Bare explanations, on the other hand, are “naked”: they do not hold in virtue of anything else. Some successful explanations would have to be unbacked for the regress worry to be avoided.

Bare explanations are controversial in themselves but, more importantly, they seem to be in tension with separatism. This is a significant cost for (B=E). Separatism wants to capture the intuition that successful explanations are higher-order, macro, phenomena that do not “float-free.” Bare explanations go against this intuition. To be clear, I am not claiming that the existence of bare explanations is incompatible with separatism. If separatism is construed minimally as the thesis that explanations are separate from their backers, then bare explanations do not pose a threat (bracketing their controversial nature). My point is that positing successful unbacked explanations is in tension with a philosophically attractive version of separatism. Such a view would say that every successful explanation is backed, in the same way physicalists say that every state is nothing over and above a physical state. In this sense, proponents of (B=E) who wish to argue that only some successful explanations are explained need to adopt an unattractive version of separatism.Footnote ²²

4. Backing as grounding

The natural alternative to (B=E) is the view that backing is a form of grounding. As previously noted, explanations hold in virtue of the facts that back them. Since in-virtue-of talk and priority-talk are often taken to be indicators for the existence of grounding relations, backing-as-grounding is a view that deserves consideration:

Saying that the explanation of a mental state in terms of its corresponding brain state is backed by the relevant grounding-fact means that the former is grounded by the latter. Still, the proponent of (B=G) needs to do a lot of additional work in order to make (B=G) an illuminating definition of backing.

Before critically evaluating (B=G), I should make the following clarification. The most developed version of (B=G) has been recently proposed by Sjölin Wirling (Reference Sjölin Wirling2020).Footnote ²³ However, her account is different from my understanding of (B=G) in two ways. First, as already noted, she takes backing to relate facts of the form [A grounds B] with facts concerning the explanatoriness of the proposition ‘A explains B.’ Secondly, she defines backing as partial grounding.

I have addressed the first point in section 2. Concerning the second point, I agree with Sjölin Wirling that if backing is a form of grounding, then grounding-facts partially ground their corresponding explanations.Footnote ²⁴ It is plausible that for an explanation’s success conditions to be fulfilled certain epistemic/pragmatic conditions should also be in place (in addition to the relevant grounding-facts). But I see no reason to insist that the first relatum of backing should always be a grounding-fact. In this sense, these epistemic/pragmatic conditions would also be partial grounds. And such conditions together with the relevant grounding-fact would fully ground the relevant explanation. In this sense, backing can’t be defined as partial grounding since there are clear instances of backing being underwritten by full grounding relations (i.e., the ones involving the conjunction of a grounding-fact with its appropriate epistemic/pragmatic conditions).Footnote ²⁵

That being said, I take these two differences to not be particularly important. The core of Sjölin Wirling’s theory (i.e., that backing is a form of grounding) is independent from these auxiliary assumptions and deserves serious consideration. Also, as it will become apparent, the challenges I will raise against (B=G) also apply to Sjölin Wirling’s specific view. For this reason, my focus on (B=G) is dialectically acceptable.

Appeals to grounding can be understood in many ways. I will divide them into two groups: reductive and nonreductive accounts. The nonreductive view takes grounding to be primitive (Audi Reference Audi2012). Proponents of this view argue that grounding resists analysis but is still a valuable metaphysical tool. Perhaps the most important merit of this view is that it can accommodate the thesis that every successful explanation is backed without generating a regress. The resulting picture would simply be the view that every successful explanation is grounded.

Still, nonreductive versions of (B=G) have an important shortcoming: they are uninformative. First, if grounding is primitive and backing is a form of grounding, then (B=G) simply collapses to the view that backing is ultimately unanalyzable.Footnote ²⁶ In this sense, it simply is not illuminating enough to say that backing is a form of grounding. Instead, we should prefer views which reduce backing to more familiar phenomena. Secondly, the grounding literature is still relatively young in comparison to other literatures. This unsurprisingly leads to a lack of consensus concerning many of the features of grounding (cf. Rodriguez-Pereyra Reference Rodriguez-Pereyra2015). In this sense, it would be better to appeal to a less controversial entity when we wish to define backing.

At this point it could be objected that, for separatists, the existence of grounding is already assumed. In this sense, separatists would not take grounding to be unfamiliar. This is certainly true for some separatists. But, as noted in section 1, backing is a phenomenon that appears in other domains as well (e.g., causal explanation). One needn’t believe in the existence of grounding in order to be a separatist. In this sense, a separatist about causal explanation who is also a grounding-skeptic would find (B=G) unconvincing.

Finally, another way to illustrate the fact that (B=G) is uninformative is by considering that a characterization of grounding in terms of backing would be explanatorily underwhelming.Footnote ²⁷ Even if one does not aim to define grounding in terms of its backing role toward explanation, it would be nice to be able to characterize grounding in terms of its function. Grounding is the relation that, among other things, backs explanations. If backing is a form of grounding, then that way of illuminating grounding would not be available anymore.

I should note that I agree with Sjölin Wirling (Reference Sjölin Wirling2020, 7) that a circular characterization of grounding is permissible. She presents the following case: the property of being a blood relative is realized by the property of parenthood. But it is plausible that in characterizing blood relatedness, one would refer to the property of parenthood. Indeed, it would not “obstruct understanding” (Sjölin Wirling [Reference Sjölin Wirling2020, 7]; my emphasis) to say that grounding is that which grounds certain kinds of explanations. My weaker point is that it would be desirable to be able to illuminate grounding in this additional way (i.e., by appealing to its function to back explanations). In this sense, a characterization of grounding in terms of backing qua grounding would be uninformative (albeit, possible).

What about reductive versions of grounding? A promising way of reducing grounding is by appealing to the set of, what Wilson calls, “small-g” relations (Reference Wilson2014). A small-g relation is, roughly, a determination relation that has a very similar profile to grounding. For example, the relation of constitution is also said to capture priority-talk and is also taken to be explanatory.

A reductive account of grounding in terms of small-g relations can be articulated in two ways. The first one would be to say that backing is a form of grounding and grounding is multiply realizable by different small-g relations (J. Wilson Reference Wilson2014, 567-8; Rettler Reference Rettler2017). In this sense, backing would be identical to the realized entity which would entail that backing itself is multiply realizable by small-g relations.Footnote ²⁸ This option is very implausible. Many paradigmatic small-g relations are not plausible realizers of backing (e.g., set-formation).

A more promising way of understanding backing as a kind of reduced grounding is by taking backing to be identical to one of the (potentially many) realizers of grounding. In this sense, (B=G) would be the view that backing is identical to some small-g relation. Still, it is impossible to assess this proposal without specifying which small-g relation backing is supposed to be. For this reason, (B=G) is unilluminating and, at best, only the first step toward an informative definition of backing.

5. Backing as truthmaking

In this section, I propose a new definition of backing. According to (Functional), the backing relation connects grounding-facts with explanations. Also, explanations, as mentioned in section 2, are certain kinds of propositions. But what kind of relation connects propositions with grounding-facts? A very plausible candidate for this role is the truthmaking relation.

(B=T) satisfies all three clauses of (Functional). It is a nontrivial and substantive issue whether a given worldly fact serves as a truthmaker for a proposition. Also, truthmaking is a cross-categorical relation par excellence (Tahko Reference Tahko and Calemi2016). Finally, it is plausible that in order for an explanation to be successful it is (at least) necessary for that explanation to be true.

What is the nature of the truthmaking relation? According to Armstrong’s (Reference Armstrong2004) classic picture, truthmaking is the internal relation of necessitation. As a quick example, take the following psychophysical explanation:

What backs (M)? Plausibly, worldly facts such as the relevant psychophysical law partially grounding the fact that Mary has mental state M₁. Adopting Armstrong’s account, this means that Mary’s brain state B₁ together with the relevant psychophysical law necessitate the truth of (M). On the face of it this seems plausible. Of course, there are well known objections to the view that truthmaking is the relation of necessitation, which I am not going to rehearse here (MacBride Reference MacBride2020, sec. 1.2.). Thankfully, (B=T), on its own, takes no particular stance toward the specifics of the truthmaking relation. In this sense, I intend for my proposal to be minimal. Truthmaking, in this context, is supposed to designate whichever relation is posited by one’s background truthmaker theory.

Deferring to one’s background truthmaker theory is dialectically acceptable. Figuring out which truthmaker theory is the correct one is a substantive philosophical problem that requires our attention anyway, independently of the discussion around backing, grounding, and the separatism/unionism debate. In this sense, the fact that the final details of my proposal are “hostage” to one’s background truthmaker theory is not a significant cost.Footnote ²⁹

The minimality of (B=T) is worth emphasizing in at least three additional ways. For one, nothing in (B=T) entails a robust notion of truthmakers. Opponents of truthmaker theory usually argue that one can make sense of truth being dependent on reality without having to posit separate entities called “truthmakers.” (B=T) is neutral toward this objection. One is free to adopt a thin understanding of truthmakers according to which such entities are not separate and distinct facts but are simply those bits of reality that account for the truth of the relevant proposition.Footnote ³⁰

Secondly, there is an ongoing discussion about the level of grain of the truthmaking relation. For example, some opponents of the correspondence theory of truth argue that a robust understanding of correspondence (perhaps, as causal regulation) is explanatorily superfluous. Again, (B=T) is neutral toward this discussion. Following Armstrong, proponents of (B=T) can take the truthmaking relation to be an internal relation without reifying it by appealing to some external determination relation.

Thirdly, so far, I have been focusing on backing as a relation that holds between explanations and grounding-facts. But, as mentioned in section 2, there is no reason why backing should be constrained in this way. Truthmaking, as such, can be used to define diverse metaphysical theses (from antirealism to realism about a given domain). Analogously, an explanation could be backed by determination-facts (broadly construed), nomic facts, or facts about essences. But they could also be backed by facts which are not worldly, at least in the traditional sense. For example, it could turn out that explanations are true in virtue of the fact that they are appropriately related to other explanations. In a case like this, such explanations would be backed by the fact that they figure in an appropriately defined set of explanations.Footnote ³¹

Finally, (B=T) is more informative than both construals of (B=G) while staying minimal toward the details of the truthmaking relation itself and pluralistic concerning the different kinds of entities that can serve as truthmakers. In this sense, (B=T) could be compatible with (B=G) if one takes grounding to be reducible and truthmaking to be one of its realizers. Still, such assumptions are controversial, and I take it that (B=T) has merit independently of its connection to grounding. This is particularly evident if one considers that skepticism about truthmaking is, in general, more controversial (and less widespread) than skepticism about grounding. As mentioned, grounding is a relatively new metaphysical tool whereas my notion of truthmaking is minimal. Under these considerations, I take it that (B=T) should be the default view concerning the nature of the backing relation. In the following two sections, I consider two objections against my view.

6. The inheritance worry

Grounding theorists often appeal to the nature of explanation to justify the fact that grounding has certain formal features. Grounding is supposed to be irreflexive because explanation is irreflexive (grounding inherits its formal features from explanation) (Maurin Reference Maurin2019). However, it could be objected that (B=T) is implausible because the truthmaking relation (in any of its forms) cannot plausibly fulfill the inheritance function. Specifically, it is implausible that truthbearers have the same formal features as their truthmakers.

To illustrate, compare truthmaking to relations that plausibly do license inheritance claims. The identity relation is the most obvious example. If explanations are identical to grounding-facts, then it follows that they have the same formal features. A less trivial case can be found in the literature on mental causation. Some philosophers argue that mental states hold in virtue of brain states and, because of that, the causal profile of the latter is transmitted to the former.Footnote ³² But backing is neither the identity relation nor the relation that holds between minds and brains.

There are two ways in which (B=T) can be defended against this. The first strategy involves directly meeting the challenge by arguing that truthmaking can license inheritance claims. To that effect, it could be claimed that truthmaking should be understood as an isomorphic relation. More specifically, truthmaking could be isomorphic in the sense that truthbearers are structurally identical to their corresponding truthmakers. The proposition that the cat is on the mat involves a certain relation between its constituents that “mirrors” the structure of the fact that the cat is on the mat. If this is true, then those explanations that are backed plausibly share the same formal features with the grounding-facts that back them.

Against this move, it should be noted that knowing about the features of explanation cannot tell us anything about grounding-facts that do not serve as truthmakers. Looking into the features of explanation (asymmetry, irreflexivity, etc.) can only serve to illuminate the features of those (and only those) grounding-facts which back explanations. In this sense, even if one assumes that truthmaking is isomorphic, this at best provides only limited access to the inner workings of grounding. Also, the very claim that truthmaking is isomorphic is far from obviously true (Schipper Reference Schipper2020).

So far, I have been mostly focusing on how explanations relate to their corresponding grounding or determination-facts. But, as previously mentioned, there is no good reason to restrict backing in this way. Backing is supposed to be the relation that connects explanations with whichever entity makes them true. Assuming isomorphism would beg the question against views that allow for successful explanations to be true but cash out their success holistically (to mention one example). Such views would say that an explanation of the form ‘A explains B’ is not made true by a grounding-fact of the form [A grounds B] but by a plurality of different facts that bear no isomorphic relation to the original explanation.

My preferred strategy involves denying that we should expect to find out about the nature of grounding by looking at the explanations which grounding-facts back. Grounding should be examined in the same way every other phenomenon is examined: by hypothesizing and testing such hypotheses against a background of a well-established body of beliefs. The analogy with causation is helpful at this point.Footnote ³³ It is uncontroversial that there are causal events which are not explanatory. Still, there are other ways in which philosophers have proceeded to learn about the nature of causation. Being able to back causal explanations is one of the roles that causal relations have. Other roles include, for example, figuring in our best scientific and folk theories. Philosophers, based on certain folk and scientific platitudes about causation, propose certain hypotheses about what the causal relation really is (e.g., counterfactual dependence, energy transfer, etc.). At best, looking into the nature of causal explanations can be one of the many ways in which we can uncover the true nature of causation.

7. The regress worry

Recall that one of my worries against (B=E) was that given (Explanation Maximalism), a regress is generated. (B=T) is supposed to avoid this worry. But it could be plausibly argued that (B=T) also leads to a regress if one takes truthmaking to be an explanatory relation. If truthmaking is explanatory, then (B=T) seems to collapse into (B=E). A way to raise this worry is to take truthmaking to be a form of grounding and then take grounding to be explanatory. But the objector does not even need to make this move.Footnote ³⁴ The link between truthmaking and explanation is usually highlighted in the relevant literature, so I take the claim that truthmaking is explanatory to be well-motivated independently of whether it is a grounding relation.

What does it mean to say that truthmaking is explanatory? Asay (Reference Asay2017, 10) identifies two possible answers: either truthmaking is itself an instance of the explanation-relation or explanation is simply a constraint on truthmaking (i.e., P makes <P> true only if P explains <P>). The first option is a form of unionism about truthmaking whereas the second is a form of separatism about truthmaking.

Ruling out the first option seems fairly easy. It is simply bizarre to be a separatist about grounding and a unionist about truthmaking. Even if one does not take truthmaking to be a form of grounding, it could still be argued that the two notions are similar enough. So, separatism can be motivated for both relations on similar grounds.

Is grounding similar to truthmaking? It is not obvious that it is. As previously mentioned, it is controversial that truthmaking is a form of grounding. Perhaps, as Audi (Reference Audi2019) notes, truthmaking is not a grounding relation because it should not be understood as a determination relation. But if that’s the case, then the putative similarity between the two relations becomes thin. Against this, I propose that separatism about both grounding and truthmaking should be motivated differently. Rather, separatism is primarily a view about explanation. Successful explanations are certain kinds of propositions which do not float free. So, insofar as one is a separatist about explanations involving grounding one should also be a separatist about explanations involving truthmaking. In other words, separatism about grounding and truthmaking are simply instances of separatism simpliciter.

The second option is trickier. According to this form of separatism, truthmaking and explanation are distinct, but every truthmaking-fact ([P makes <P> true]) has a corresponding explanation (<P explains <P>>). This version of separatism is different from the kind of separatism I have been considering so far (call my version, standard separatism). An important and desirable feature of standard separatism is that grounding-facts can exist in the absence of explanation. In an analogous sense, separatism about truthmaking should allow for certain truthmaking-facts to exist in the absence of a corresponding explanation. Does this compromise the well-established link between truthmaking and explanation? It does not. It can still be said that truthmaking is explanatory even if it is not the case that every truthmaking-fact figures into an explanation. Causation is also explanatory by anyone’s lights even though there are clear cases of causal events which are not involved in causal explanation.

Still, one could wonder whether standard versions of separatism coupled with (B=T) can successfully deal with the regress worry. Can truthmaking-facts exist in the absence of explanation? In essence, the answer to this question depends on one’s view about the ontological status of explanations (i.e., the ontological status of propositions). According to one influential view, propositions are reified abstracta that are expressed by particular sentences. Such views take explanations to be stance independent in the sense that explanations exist independently of whether they are expressed or conceived by agents. But if that’s the case, then the regress worry looms large again. Every truthmaking-fact would have a real, stance independent, corresponding explanation. Such truthmaking-facts (e.g., the fact that [P makes <P> true] makes <P explains <P>> true) would, in turn, have their own corresponding explanations, and so on ad infinitum. So, it seems that (B=T) faces the same worry as (B=E) in terms of generating regresses.

One thing to immediately notice is that even if we accept that (B=T) generates a regress, the kind of regress it generates is significantly different from the one (B=E) generates. (B=E) coupled with the thesis that every explanation is backed entails that every explanation is explained. This means that if an explanation exists, then an infinite series of explanations is generated. Under closer inspection, this is a regress that runs “downward.” A second-order explanation is more “fundamental” than the explanation it explains (in the sense that first-order explanations depend on second-order explanation, second-order explanations depend on third-order explanations, and so on ad infinitum). This means that the infinite regress (B=E) generates runs toward the fundamental level. (B=T), on the other hand, leads to an “upward” regress. In this case, the first element of the series is a truthmaking-fact which, in turn, gives rise to another truthmaking-fact, and so on ad infinitum. This means that the order of dependence goes from a truthmaking-fact (of the form [P makes <P> true]) toward its corresponding “meta” truthmaking-fact (of the form [[P makes <P> true] makes <P makes <P> true> true]). This is a significant difference because upward regresses are generally regarded as less problematic than downward regresses (Cameron Reference Cameron2008).

Still, it should be noted that there is a way for the separatist to deny that (B=T) generates a regress altogether. Specifically, the separatist should deny that propositions exist stance independently.Footnote ³⁵ Notice that if the existence of explanations directly depends on the deliberation of conscious agents, then there will not be an infinite series of explanations unless an agent can generate one. If a truthmaking-fact makes its corresponding explanation true, this presupposes that that explanation exists. The demand for a truthmaker arises only once the relevant proposition is formed. But according to the view I am considering, whether an explanation is formed depends on the relevant agents and their explanatory demands. To compare, (B=E) faces a regress worry that cannot be avoided using similar means. It is independently plausible that every successful explanation requires a backer. (B=T) can meet that demand: explanations, insofar as they are formed, require truthmakers. Rather, the proponent of (B=T) should deny the converse thesis, namely, that every truthmaker has a corresponding explanation.Footnote ³⁶

I do not have the space to fully defend a stance-dependent view about the existence of propositions. Still, it suffices to say that such a view is both powerful and already assumed by many philosophers working on explanation. Kim (Reference Kim1988), for example, adopts a view of propositions akin to contemporary conceptualist theories (i.e., propositions as abstractions of mental tokenings) (King Reference King2007).Footnote ³⁷ The alternative would be to understand propositions as entities whose existence-conditions are completely independent of human agency. But such views are notorious for their inability to explain how they get their truth-conditions and their representational capacities. In comparison, the agent-dependent view has a clear-cut explanation: propositions get their truth-conditions and their ability to represent in virtue of the capacities of conscious agents.

There are ways to resist these points, but it should be noted that whichever way the relevant dialectic plays out, at least as far as regresses are concerned, (B=T) is superior to (B=E). If (B=T) generates a regress, then it is a regress that is more palatable than the one (B=E) generates. Finally, I have highlighted a plausible, albeit not completely nonparochial, way for the proponent of standard separatism to completely bypass the regress worry.

A final point about (B=T) and regresses. I have argued that (B=E) leads to a downward regress, whereas (B=T) leads to an upward one. But it could be argued that (B=T) leads to a downward regress as well. After all, we can still ask: What explains why [A grounds B] makes ‘A explains B’ true? And, then, we can ask what explains that further truthmaking-fact ad infinitum. In this sense, (B=T) might not be superior to (B=E) in that regard after all.

Note that in order for (B=T) to generate a regress in the above sense, (B=T) needs to be coupled with the two following triggering statements:Footnote ³⁸

1. (1) Every truthmaking-fact has a ground.

2. (2) Every grounding-fact involving a truthmaking-fact (of the form “P grounds the fact that Q makes <Q> true”) has a corresponding explanation (of the form “P explains the fact that Q makes <Q> true”).

Both statements can be contested. (2) presumably follows from the principle that determination-facts always have explanations which they back. But I have already indicated that an attractive version of separatism would want to accept the possibility of determination-facts occurring in the absence of explanation. I also proposed a plausible way to deliver this result by taking propositions to be stance-independent entities.

(1) can also be resisted. Even if some truthmaking-facts have grounds, it is not obvious that this should apply to every truthmaking-fact. For all we know, some truthmaking-facts might be brute or fundamental. Perhaps (1) can be motivated by appealing to a principle of sufficient reason according to which everything has a ground. Compare with (B=E). The triggering statement that (B=E) needs to be coupled with is, as noted, simply a plausible version of separatism: “Every successful explanation is backed.” But, surely, that principle is much less controversial than the principle that everything has a ground.

Separatism coupled with (B=T) entails that every successful explanation has a truthmaker, whereas separatism coupled with (B=E) entails that every successful explanation needs to be explained (which results in a regress). For this reason, the downward regress problem is avoided by (B=T) and is particularly pressing for the proponent of (B=E).Footnote ³⁹