Inside the minds of humans and other animals

Plants don't think – but animals do. The difference between the thoughts of humans and the thoughts of other animals – and whether we will ever be able to find out exactly what they are - will be the topic of a public lecture given this evening by a Cambridge philosopher.

While scientists spend their time in laboratories, philosophers spend their time thinking. Professor Tim Crane, the new Knightsbridge Professor of Philosophy, specializes in thinking about thought. For example: what are the essential features of anything that counts as thought? What is it to be conscious? What is it like to be a dog?

For the last 20 years Crane has been working on these abstract questions about thought and consciousness and he is best known for his book Elements of Mind (2001).

Recently, he has been focusing on the difference between the thoughts of humans and the thoughts of other animals - not just on what they think about and how we know about it, but also on what kinds of thought are available to them. These topics will be a strand of his next book, The Objects of Thought, due out in 2012, and will be central to next week's talk.

"Asked what makes the human mind different from the minds of other animals, many people might come up with the answer: it must be language. And many of them will say that the explanation for why we have language is to enable communication," says Crane.

"But other animals do communicate, of course, sometimes to convey messages about their environment. For example, vervet monkeys use one call to alert the troupe to the presence of a leopard and another to the presence of an eagle. So if animals communicate quite complex messages without language, what does language add?"

Crane will argue next week that one of the most distinctive things about human thought is our capacity for speculating about things that don't affect us directly. And he suggests that it is this, rather than any specific need to communicate, which explains the role language plays in our thinking.

While animal communication is based on immediate need - and rooted in the drive for survival - people are preoccupied with all kinds of questions that have no obvious practical benefits. For example, for millennia people have been fascinated by the age and size of the universe. Although this may have developed out of an interest in using the stars for navigation and so on, it became an interest in its own right, a consuming passion for both cosmologists and amateur star-gazers.

This kind of preoccupation is distinctively human and, Crane argues, irreducible to other more basic kinds of thought - we cannot explain people's interest in watching the skies in terms of (say) simple desires for food, comfort and sex.

Aristotle famously said that everyone by nature desires to know. Crane suggests that this fascination with speculation, the acquisition of knowledge for its own sake, is the key to understanding the distinctiveness of human thought and language. Indeed, although we are ignorant of the origins of language, it may be that the desire to store, organise and share thoughts is what pushed us to devise complex language in the first place, he believes.

As a philosopher Crane is less concerned with the "how" (for example, understanding the nuts and bolts of the brain) than with the more knotty subject of the "what" (the most general features or 'essence' of mind). He understands the mind in terms of the idea of a perspective or a point of view.

"A plant is alive, but it doesn't have a perspective on its life, while a dog certainly does. Like us, dogs perceive, they desire, they remember and they pursue their goals; this is all part of having a perspective," Crane says. "But our kind of perspective on the world is also very different from a dog's, and so to get a proper understanding of our minds, we need to describe in the most general way what these differences are."

Crane doubts that our distinctive capacity for thought can be completely explained in terms of evolution by natural selection, with intellectual curiosity being simply a result of being rewarded by improved survival chances. But neither does he opt for a religious explanation with human braininess being God-given.

Instead he argues that these are not the only options: we can also understand human thought as something genuinely novel which developed somehow out of more primitive kinds of thought, without being reducible to those other kinds of thought.

For this reason, he looks at evidence from animal psychology and from human developmental psychology to support his conjectures about the nature of human thought. 'No-one really knows what 'the' philosophical method is, or what makes a question "philosophical" rather than "scientific". So there should be no boundaries to the kinds of evidence we should consider in forming our philosophical theories.'

But Crane nonetheless diverges sharply from some animal and comparative psychologists whose work he uses. "Scientists work by taking incremental steps and they are sometimes reluctant to make bold hypotheses. Philosophy can sometimes suggest such hypotheses, which may be confirmed or refuted by later science."

But although he thinks we can make some progress in understanding how animal and human thought differ, the exact nature of animal consciousness remains deeply puzzling. "While we can get an inkling of what it might be like to be another person, and experiencing their thoughts, we really don't know what it's like to be a dog. We know that dogs feel pain and pleasure, and that they don't speculate about things like geometry or metaphysics. But the nature of their inner lives is still a mystery to us."