1. In a passage, much quoted with approval, Bentham writes, ‘The question is not, Can they reason? nor, Can they talk? but, Can they suffer?’ Bentham should not be read as suggesting that the fact that a creature can talk is never relevant to how it is to be treated. He would, presumably, have acknowledged that the possibilities of my causing another pleasure or pain are transformed by the fact that we speak a common language, and might have endorsed the widely defended view that the possession of a language creates the possibility of certain thoughts, and so of forms of pleasurable or painful emotions, that are absent without it. Bentham's point, then, will be that an ability to talk is of no ethical significance in itself. It is only by way of its connection with something else that a capacity for speech might have a bearing on how a creature should be treated.

That general claim is, I believe, widely shared. It comes in two broad forms. We may suppose that a capacity for speech is a reflection of something in a creature that makes it deserving of special forms of concern or respect, or we may suppose that the possession of language creates certain possibilities for a creature that are relevant to our treatment of it – possibilities, for example, of certain forms of suffering.

An idea of the first form is, perhaps, clear in the following remark by Aristotle:

Similarly, though with a different emphasis, the Stoics argued that ‘it is not uttered speech but internal speech by which man differs from non-rational animals; for crows and parrots and jays utter articulate sounds’.