2.1 Constraints on the GDP of accounts of design

By systematically exploring the set-theoretical relations that can exist between the G-, D- and P-sets of accounts, one can categorise them as conservative, progressive and futuristic accounts of design. Before giving this categorisation I chart the constraints on these relations.

The D-set is a subset of the G-set, for it would be inconsistent if an account accepts actual practices as types of design practices while simultaneously not acknowledging them as types of design practices. So a first constraint on the GDP of an account is that $\text{D}\subseteq \text{G}$ .

In a similar way it follows that the P-set is a subset of G, leading to the constraint $\text{P}\subseteq \text{G}$ . This constraint can be strengthened if it is assumed that the prescription by an account is not trivial, that is, that an account does not take all possible types of design practices as favourable. This assumption means that designers are prescribed to carry out specific type of design practices and should avoid other types. Hence, there then exist types of design practices in G that are not in P, which means in turn that P cannot be equal to G, but is a proper subset of G, so $\text{P}\subset \text{G}$ . This is a second constraint.

If it is also assumed that the prescription by an account implies that designers should change their actual design practices, then a third constraint becomes available. Such prescription implies that some types of actual design practices are not favourable types. The D-set is then not a subset of P, leading to a constraint that it is not the case that $\text{D}\subseteq \text{P}$ : there are types of actually design practices in D that designers should abandon by the account since they are not types of design practices in P that the account prescribesFootnote ³ .

The first constraint $\text{D}\subseteq \text{G}$ holds necessarily: if an account takes a type of actual practices as design, it acknowledges it as a type of design practices. The second and third constraints depend however on the two assumptions described in the previous two paragraphs. In the ideal case that all actual design practices are of the types that are prescribed in an account, one has that $\text{D}\subseteq \text{P}$ . Moreover, in the trivial case that an account prescribes all types of design practices, one has $\text{P}\subseteq \text{G}$ . Imposing the second and third constraints on accounts of design thus expresses that the prescription by accounts is non-trivial, and that designing has not yet evolved to the ideal case in which all actual design practices are of the prescribed types of favourable practices.

Consider, for instance, an account in which it is observed that actual design practices sometimes fail to produce eco-friendly design solutions, and in which the prescribed types of design practices do lead to eco-friendly solutions. All types of observed actual design practices, including those that produce eco-friendly solutions and those that do not, are in the account taken as design practices, which is captured by the first constraint: $\text{D}\subseteq \text{G}$ . All prescribed types of design practices that produce eco-friendly design solutions, are also general types of design practices but some general types of design practice do not produce eco-friendly solutions, which is captured by the second constraint: $\text{P}\subset \text{G}$ . Finally, since designers are by this account sometimes actually producing non-eco-friendly design solutions, there is at least one type of actual design practices that is not a prescribed type of design practices, which is expressed by the third constraint: it is not the case that $\text{D}\subseteq \text{P}$ .

The three constraints on the GDP of accounts are summarised in Table 2.

2.2 Conservative, progressive and futuristic accounts of design

Consider the G-, D- and P-sets of an account by means of Venn diagrams. Constraints 1 and 2 ( $\text{D}\subseteq \text{G}$ and $\text{P}\subset \text{G}$ ) imply that G is always represented by the biggest diagram. There are now ten possibilities for D and P lying within G, depicted in the Figures 1–4. Constraints 2 and 3 ( $\text{P}\subset \text{G}$ and the impossibility that $\text{D}\subseteq \text{P}$ ) rule out the four possibilities given in Figure 1: P should not be as big as G ( $\text{P}\subset \text{G}$ should not be violated); and D cannot be equal to P or lie within P (it is impossible that $\text{D}\subseteq \text{P}$ ). The ruled-out GDP possibilities represent accounts in which the D-set describing types of actual design practices, is in or is equal to the P-set of prescribed types of design practices, hence represent the ruled-out ideal case that all actual design is favourable design. Possibilities 2 and 4 represent moreover the trivial case that all possible design practices are favourable.

Figure 1. The ruled-out GDP possibilities 1, 2, 3 and 4; $\varnothing$ is the empty set, such that $\text{G}=\text{P}$ for possibilities 2 and 4.

Two GDP possibilities that are allowed are characterised by P lying within D, see Figure 2. These possibilities 5 and 6 represent accounts that may be called conservative, for in accounts in which P lies within D, prescribed types of favourable design practices are always types of actual design practices; there is thus not a type of favourable design practices that has not yet been realised in actual design. Accounts in which the expert position is adopted may be cases in point, since on such accounts types of actual design practices by experts are taken as types that are to be prescribed (but this categorisation is qualified in the next section).

Figure 2. The conservative GDP possibilities 5 and 6; $\varnothing$ is the empty set, such that $\text{G}=\text{D}$ for possibility 6.

Two further possibilities 7 and 8 allowed by the constraints are characterised by D and P partly overlapping, see Figure 3. Accounts that are instances of these possibilities may be called progressive, for in such accounts there are types of favourable design practices that are already adopted in actual design, and there are such practices that are not (yet) adopted. By such accounts there can thus be progress: there are new ways of designing available that are (also) favourable. The theory of axiomatic design (Suh Reference Suh2001) may be an example of such a progressive account that prescribes types of design practices that have already been carried out and types of design practices that are new.

Figure 3. The progressive GDP possibilities 7 and 8; $\varnothing$ is the empty set, such that $\text{G}=\text{D}\cup \text{P}$ for possibility 8.

The final two allowed GDP possibilities 9 and 10 are characterised by D and P not overlapping, see Figure 4. In accounts falling under these possibilities all types of actual design practices are not types of favourable design practices that are prescribed. Yet types of favourable design practices exist and may in the future become actual. Let us call these accounts futuristic accounts. The introduction of the first design methods at the time when artisan production ruled, may be reconstructed as such futurism: existing artisan practices are discarded as unfavourable and new types of design practices that are considered to be favourable are made available.

Figure 4. The futuristic GDP possibilities 9 and 10; $\varnothing$ is the empty set, such that $\text{G}=\text{D}\cup \text{P}$ for possibility 10.

3.1 The strict and liberal expert positions

Consider accounts of design in which the expert position is adopted. In such accounts some designers are taken as experts and a number of their practices are singled out as favourable. Let these expert design practices be $\{e_{1},e_{2},\ldots ,e_{n}\}$ . The expert practices are then analysed as having certain shared characteristic factors, let us call them the x-factors. These $x$ -factors define types of expert design practices, and let X be the set that contains these types of practicesFootnote ⁴ . The types of expert practices in X are finally prescribed in the accounts to all designers as the types of favourable design practices.

When approached within the GDP categorisation, the expert position leads to two general constraints. First, since on this position the prescribed types of design practices are the types of expert practices in X, it follows that X is equal to the P-set. Second, since the singled-out expert design practices $\{e_{1},e_{2},\ldots ,e_{n}\}$ are instances of the types of expert practices in X, and since these practices $\{e_{1},e_{2},\ldots ,e_{n}\}$ have all been actually displayed, it follows that their types are also in the D-set, meaning that the overlap between X and D cannot be empty. Formally this means $\text{X}=\text{P}$ and $\text{X}\cap \text{D}\neq \varnothing$ . The latter constraint allows that the X-set contains types of design practices that are not in D and hence not (yet) actually carried out. That this possibility is possible on the expert position becomes clear below when discussing the liberal expert position.

In a strict reading of the expert position the X-set does not contain other types of design practices than those of which the singled-out expert practices $\{e_{1},e_{2},\ldots ,e_{n}\}$ are instances. The $x$ -factors describing X then characterise only the types of practices as displayed by the expert designers, and no other types of practices that resemble $\{e_{1},e_{2},\ldots ,e_{n}\}$ . For instance, one carefully analyses what expert designers in product design or in industrial innovation do (e.g., Cross Reference Cross2006; Verganti Reference Verganti2009) and then this precise description defines what other designers should do for mimicking the successes of the experts. With this precise description of the expert design practices, X will only contain types of design practices that have already been carried out. Hence, on the strict expert position X is a subset of D, or $\text{X}\subset \text{D}$ .

A more liberal reading of the expert position is also possible and amounts to allowing in X types of design practices that have not yet been exercised. The analysis of the expert design practices $\{e_{1},e_{2},\ldots ,e_{n}\}$ could still be as precise as in the strict expert position, and lead to a detailed description in terms of $x$ -factors of the types of design practices that have $\{e_{1},e_{2},\ldots ,e_{n}\}$ as instances. Yet, by generalising over this description by letting some $x$ -factors have multiple values, the X-set can contain more types of design practices than only those that have $\{e_{1},e_{2},\ldots ,e_{n}\}$ as instances. Say, the experts may all have been sketching with pencils to explore their initial ideas, but it may be judged on the liberal expert position that the use of in particular pencils is not relevant to the favourability of the singled-out practices $\{e_{1},e_{2},\ldots ,e_{n}\}$ . The X-set then contains types of favourable design practices in which exploration is done by pencil or by other means, and expert designers need not yet have exercised the latter in reality. Or the expert practices $\{e_{1},e_{2},\ldots ,e_{n}\}$ may all have been practices in product design, yet the prescription may also concern other application domains, such that X also contains types of practices in social and policy design (e.g., Dorst Reference Dorst2015). And this transposition of design thinking to other domains may again lead to allowing types of design practices that have never been done actually. Hence, on the liberal expert position X need not be a subset of D.

In Table 3, the constraints for the expert position and its two readings are listed. With these constraints it follows that the suggestion of conservatism is indeed confirmed for accounts in which the expert position is adopted in its strict reading, but not for accounts based on the liberal reading. In terms of the GDP categorisation the strict expert position leads to accounts that are always conservative. The possibilities 7 to 10 are ruled out because when in the diagrams given in Figures 3 and 4 the P-set is equated with X, one obtains diagrams in which X is not a proper subset of D, which is not allowed by the strict expert position constraint $\text{X}\subset \text{D}$ . The conservative possibilities 5 and 6 as given in Figure 2 however give diagrams in which the expert position constraint is met, leading to two GDP options for the strict expert position (see Figure 5).

Figure 5. The two options for the strict expert position, through GDP possibilities 5 and 6.

Since these two options are instances of the possibilities 5 and 6, it follows that the strict expert position is indeed conservative: it leads to accounts in which the prescribed types of favourable design practices are always types of actual design practices.

For accounts in which the liberal expert position is adopted, the possibilities 9 and 10 are still ruled out due to the general constraint for the expert position ( $\text{X}\cap \text{D}\neq \varnothing$ ; see Table 3) that some of the prescribed types of design practices in X are types that have actually been done by designers (namely the types corresponding to the singled-out expert practices $\{e_{1},e_{2},\ldots ,e_{n}\}$ ). But the other possibilities 5 to 8 are now available, leading to four options for the liberal expert position, as given in Figure 6.

Figure 6. Four options for the liberal expert position, through GDP possibilities 5, 6, 7 and 8.

With the options 1 and 2 the liberal reading of the expert position leads again to conservative accounts of design, yet with the options 3 and 4 one can also arrive at this reading in progressive accounts in which prescribed types of favourable design practices can be types of design practices that have no precedence yet.

3.2 Routes for adjusting the prescribed types of design practices on the expert position

The above analysis showed that on the liberal reading the expert position can lead to a progressive account of design that allows for prescribing types of design practices that have not yet been carried out by expert designers. More generally there seem to be two routes available for adjusting the types of design practices the expert position prescribes, and one of them is even open to the strict expert position. The first route is defined for the above described progressive accounts allowed by the liberal expert position. Given a fixed set of expert design practices $\{e_{1},e_{2},\ldots ,e_{n}\}$ and given a fixed $x$ -factor description of the types of practices $\{e_{1},e_{2},\ldots ,e_{n}\}$ are instance of, one can still adjust the prescribed types of design practices in X by varying the generalisation over the $x$ -factor description. One can, say, generalise over the means used for sketching, over the application domain and over other characteristics of the expert design practices $\{e_{1},e_{2},\ldots ,e_{n}\}$ . This first route for adjusting the prescription may also be suitable to incorporate design practices using new design tools: the favoured expert practices are then expanded from practices in which such tools are not used to practices in which they are used. Yet more substantial adjustments are harder to be achieved. Design practices that are envisaged by the Cradle-to-Cradle approach are difficult to construe as generalisations of earlier expert practices, for instance due to the Cradle-to-Cradle approach to see product design as part of the design of artificial ecosystems.

The first route for adjusting the types of design practices the expert position prescribes draws on the possibility to changing the contents of the X-set by generalising the $x$ -factor description of this set. The second route draws on the possibility to change the set of practices $\{e_{1},e_{2},\ldots ,e_{n}\}$ singled out as expert practices. This route is available for both the strict and liberal readings of the expert position. On both these readings one may at some point decide that new actual design practices $e_{n+1},e_{n+2},\ldots$ are also of expert quality, and possibly that some of the practices in $\{e_{1},e_{2},\ldots ,e_{n}\}$ should not be considered as of expert quality anymore. This decision would imply that the designers involved in the newly singled-out practices $e_{n+1},e_{n+2},\ldots$ are taken as experts (assuming these designers were not involved in the practices in $\{e_{1},e_{2},\ldots ,e_{n}\}$ ) and it would involve that the X-set is enriched and starts to contain also the type of design practices associated with the new practices $e_{n+1},e_{n+2},\ldots$  . This adjustment can already take place on the strict reading; on the liberal reading this adjustment can be further amplified by considering different generalisations of the $x$ -factor descriptions of the new practices $e_{n+1},e_{n+2},\ldots$  . By this second route the expert position could eventually endorse the Cradle-to-Cradle vision; as soon as design practices by McDonough, Braungart or other Cradle-to-Cradle designers are accepted as expert design, the Cradle-to-Cradle types of design practices become prescribed types. This second route is also followed when expert designers are on the expert position taken as innovators of their expert design practices. When a designer who has already contributed with a design practice $e_{j}$ to the set $\{e_{1},e_{2},\ldots ,e_{n}\}$ of expert practices, develops a design practice of a type that does not fit the X-set, then this new design practice is in principle not an expert design practice. Yet on the expert position this new design practice can be added to $\{e_{1},e_{2},\ldots ,e_{n}\}$ as a new expert practice $e_{n+1}$ , by which it becomes a design practice of a type that fits X.

The two routes towards prescribing new types of design practices are given in Table 4.

4.1 Justifying the induction assumption that types of expert design practices are favourable

The induction assumption that generalises the relation between the structure of the singled-out expert design practices $\{e_{1},e_{2},\ldots ,e_{n}\}$ and their favourability can be made precise as an assumption that the practices $\{e_{1},e_{2},\ldots ,e_{n}\}$ have a specific structure and that it is this structure that makes these practices favourable. Let the structure of these practices be captured by their descriptions in terms of the $x$ -factors, and let $f$ refer to the favourable properties for which the expert practices $\{e_{1},e_{2},\ldots ,e_{n}\}$ are singled out. Then the induction assumption is that all design practices that meet the $x$ -factors will display the favourable properties $f$ . Say, drawing from Verganti’s (Reference Verganti2009) analyses of expert design practices in firms like Alessi, the $x$ -factors are ‘collaborating with key interpreters outside the firm’, ‘open innovation-style sharing of knowledge’ and ‘restraints on return on investment-assessments’, and the $f$ properties include ‘creating innovative product families’. The induction assumption underlying Verganti’s account of design is then that all design practices that meet the mentioned $x$ -factors are ones that lead to innovative product families.

In work advancing the expert position this induction assumption is typically supported by analyses of the expert practices $\{e_{1},e_{2},\ldots ,e_{n}\}$ in which they are shown to have the favourable properties $f$ and a structure captured by the $x$ -factors. Verganti, for instance, analyses successful design practices in firms such as Alessi that did lead to innovative product families and that consisted of collaborations with key interpreters in an open innovation fashion, etc. However, such case studies can hardly count as conclusive evidence to the induction assumption; they show that there were design practices that met the $x$ -factors and that had the favourable properties $f$ , yet do not rule out that there are many other cases of design practices that also meet the $x$ -factor description but do not have $f$ . For instance, it is consistent with Verganti’s analyses that there exist large numbers of firms that have engaged in design practices similar to those of Alessi, yet failed miserably in creating innovative success.

For evaluating the tenability of the induction assumption that all the design practices that satisfy the $x$ -factors will also be displaying the favourable properties $f$ , one can logically discern three cases. First the favourable properties $f$ can be themselves $x$ -factors. The assumption is then simply a logical truth and the expert position becomes a tautology: all instances of types of expert design practices are favourable because they are all characterised by the favourable properties $f$ . This tautology typically makes the prescription useless; in cases where it still contains useful help, the prescription can be made more precise. For instance, if the $x$ -factors are merely the $f$ properties, the prescription is nothing more than the command to create an innovative product; how that is done is left unspecified. If the $x$ -factors contain more properties than $f$ , these redundant $x$ -factors are typically unnecessary constraints; the command to create an innovative product is then accompanied with additional directions because experts traditionally worked in that manner. Only if the favourable properties $f$ concern the final design outcome of the design practice and the redundant $x$ -factors concern the process of the practice, one may envisage that these redundant $x$ -factors help guide designers to arrive at the favourable outcomes; yet in that case the actual prescription seems to be that designers should follow practices that meet these redundant $x$ -factors in order to obtain the favoured innovative products, which brings us to the second case.

Second, if the $f$ properties are different to the $x$ -factors, the induction assumption can be taken to mean that the $x$ -factors make that the design practices will have $f$ , meaning that the $x$ -factors are sufficient conditions for $f$ . In this case, additional work is needed to support the assumption. The empirical basis of the expert position is that there are a number of actual expert design practices $\{e_{1},e_{2},\ldots ,e_{n}\}$ that meet the $x$ -factors and that have $f$ . This basis is insufficient for concluding that all design practices that meet the $x$ -factors have the favourable properties $f$ , as illustrated with the above example of firms that unsuccessfully copied Alessi’s innovation practices. What is needed in this second case is either a theoretical explanation that design practices that satisfy the $x$ -factors will have the favourable properties $f$ as well, or experimental results that demonstrate that this relation holds. In accounts in which the expert position is maintained, explanations why design practices meeting the $x$ -factors have $f$ are typically given in a schematic fashion. For instance, Verganti (Reference Verganti2009) explains that interaction with key interpreters opens up firms to new perspectives on existing products and technologies, and enables them to come up with innovative new uses thereof. Yet, by the lack of a sufficiently firm body of design laws and theories, such theoretical explanations may add plausibility to the induction assumption but do not prove its truth.

In the third case, the $x$ -factors do not imply $f$ but predict the presence of $f$ with some measure of certainty; there may, for instance, be stable correlations between the $x$ -factors and $f$ without there being also clear-cut logical relations. In his third case one obtains a probabilistic relation that a design practice meeting the $x$ -factors has with a specific probability $\text{p}(f)$ the favourable properties $f$ , and this probability may be small or large. Although now the induction assumption strictly speaking does not hold, the expert position still makes sense: the types of expert design practices in X can still be prescribed since they are with probability $\text{p}(f)$ favourable design practices. When, for instance, this probability is large, design practice meeting the $x$ -factors have often the favourable property $f$ , while occasional exceptions are now to be expected and not undermining the (probabilistic) induction assumption. Even when $\text{p}(f)$ is small the correlations between the $x$ -factors and $f$ may be of value; the successes of firms like Alessi can be so attractive that a probability $\text{p}(f)$ of 0,2 to repeat it with a design practice meeting the $x$ -factors is appealing enough to engage in these practices (think, e.g., of the gambles venture capitalists take). Yet, it should be noted that understanding the probability $\text{p}(f)$ in terms of quantitative numbers such as 0,2 currently does not make sense in design research; if at all, $\text{p}(f)$ can better be understood in qualitative terms such as ‘small’ and ‘large’.

The three cases are listed in Table 5. For the first the induction assumption is indeed self-evident since tautological. But in the second and third cases this self-evidence is absent. The assumption then becomes a hypothesis advancing an empirical claim. This hypothesis may be supported by argument and theory, but is in principle in need of empirical testing for corroborating it and, in the third case, for determining its precise content by (qualitatively) fixing the probability $\text{p}(f)$ .

4.2 Justifying the capability assumption that non-experts can carry out expert practices

When the induction assumption holds, then design practices in X meeting the $x$ -factors can be prescribed to other designers as practices that have the favourable properties $f$ . Yet whether these other designers can carry out the prescribed practices depends on the tenability of the second capability assumption that non-expert designers have the capabilities – the skills; the knowledge; the talents – to do so. It may seem self-evident that the expert designers themselves can carry out the practices in X, since they created them in the first place. Yet it seems equally plausible that laypersons who are not trained as designers can have severe difficulty with following these expert practices since it typically takes years of education and training to become a designer. For the expert position to make sense the question is now whether the capability assumption holds for regular designers who are not experts, for the prescription of the expert position concerns these non-expert designers.

The literature in which the expert position is embraced does not provide an unambiguous answer to this question. Regularly it seems that the answer is assumed to be positive: non-expert designers are taken as in principle able to carry out the prescribed expert design practices. In work by, for instance, Cross (Reference Cross2006), Brown (Reference Brown2009), Verganti (Reference Verganti2009) and Dorst (Reference Dorst2015), expert practices are analysed and described with the claim that all designers can profit: for non-expert designers the favourable properties $f$ are then in reach by just mimicking the experts. Experiences with non-designer professionals strengthen this positive answer since specifically in the design thinking movement, which makes expert design practices available to these other professionals, positive outcomes are reported about letting them carry out the prescribed expert design practices (e.g., in the Design SchoolsFootnote ⁵ and the Designing Out Crime organisationFootnote ⁶ ). But one can also find in the literature reasons to doubt that non-expert designers have always the ability to mimic the experts. The expert practices may be complex and subtle, and effectively be limited to only other expert designers. The expert position then does not define favourable design practices non-designers can follow, but spells out the reasons why these designers cannot engage in these favourable practices. Work by Lawson & Dorst (Reference Lawson and Dorst2009), and recently Curry (Reference Curry2014), may be taken as representing this line: it analyses in detail expert design practices, not for determining what novices and regular designers should do in their design practices, but for determining what they should learn for becoming experts themselves.

Whether or not the capability assumption holds may also depend on the types of expert design practices in X, ruling out one general answer to the question of whether non-expert designers can carry them out. Possibly this assumption can for specific types of practices be supported by argument and theory, yet in general it seems that support for the assumption again needs to come from empirical testing: in principle it seems implausible that non-expert designers can engage in expert design practices, yet a reality check with non-expert designers may prove the opposite as it already did in a number of the mentioned cases.