Since thinking, particularly rational thinking, is widely understood as the very touchstone of the human, it's unsurprising that the idea of "thinking computers" encounters considerable resistance. Surely there's "nobody at home" in a computer, and so no "subject" to do the thinking. In such as yet inconclusive debate, everything depends on what "thinking" is taken to be. So despite constraints of space affording opportunity only to present it, hardly to argue for it, let me offer my own position on that one.

First, I don't take thinking to be that which proves my existence.

Almost all professionals in the human sciences now want to distance themselves from Descartes, or at least from his "two substances": the one (the body) material; the other (the mind) non-material. There are many different versions of how to achieve such distancing. But for me, what's critical is to effect a clean break with his famous "I think, therefore I am".

It is a statement that is just plain wrong. It purports to be an argument of the form "this is the case, therefore that must be the case". But it can't be one: since he posits his "I" at the outset as subject – it is his "I" which "thinks" – he cannot legitimately conclude, with his "therefore", that he has proved its existence. He has assumed its existence in the first place so his "therefore" proved nothing. The existence of thinking in a human does not prove the existence of an "I", or "self', as its subject. So neither does the non-existence of an "I", or "self', in a computer prove that it cannot think.

But for different reasons, I would still maintain that it can't.

Humans live: computers don't. As a life-form, each human is "a distinguishable collection of matter, with – a stable configuration far from thermodynamic equilibrium". And as a consequence they have a basic interest from which all others arise: they need to maintain that "far-from-thermodynamic-equilibrium" status. For when they lose it, they die. Computers don't die.

Humans are animals: computers aren't. As members of the class animalia, each human exhibits three animal characteristics: no photosynthesis; a blastula stage in embryonic development; and directed movement. And as a consequence of their thereby actively structured relationship with their environment, they acquire some further interests: in particular, the interest of maintaining that "directed movement" characteristic for as long as possible. For when they lose it, again they die. And again, computers don't.

Humans speak: computers don't. As members of the species Homo sapiens, each human exhibits a very special "directed movement" skill: that of so directing the musculature of their six speech organs that they can produce patterned arrangements of arbitrary sounds to "linguistically represent" their environment. And as a consequence of their thereby developmentally structured relationship with that which surrounds them, they can acquire more sophisticated interests: in particular, the interest of maintaining and extending that skill. For when they can't, they cease to flourish. Computers neither flourish, nor cease to flourish.

In summary, humans live, as animals, which can speak: and computers don't. Which is why humans can think: and computers can't. For each human develops a capacity, this time unique, to internalise the spoken word into non-spoken thought: a capacity which means that they can cease merely to "inhabit" the present biosphere, but come instead to "make" the past-present-future world. If not quite Watson's "sub-vocal tremor of the larynx", thought is non-vocal language. And I believe that because we have such a linguistically structured relationship with the world around us, we acquire the most sophisticated of all our interests: we can come to love all our own kind. Computers love nothing.

So: thinking emerged to serve the metabolic, active, developmental, linguistic and loving interests of thinkers. And it's because they don't have such interests – or indeed any interests – that computers can't think.

The problem isn't – as often it's portrayed – that it's we who have made the computers. It is that, in doing so, we have made the artificial, not the synthetic. Artificial non-thinking computers do seem in many ways more useful to us than synthetic thinking copies of ourselves would be because they do things we can't. But if we were to make the synthetic – and given the ever-increasing number of synthetic amino acids accumulating in laboratory flasks, one day we probably will – then more or less definitionally, it would think. It would be "just like us". It would think "just like us". And if Vico was right to say that we only ever really understand that which we make, for humankind that could be a very good day indeed.