Penny asked:

If a visiting alien were to land in your garden and asked you what it meant for human beings to have a
mind, how would you answer? How would you decide whether the alien had a mind or that it
exercised mental functions? Would you need to posit a mind-entity to explain its behaviour?

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Ah! I must have been subconsciously thinking about your question when I responded to Mark's,
above. But there are some interesting angles here.

The first thing to say is that if the alien succeeded in making it understood that it wanted to know
'what it meant for human beings to have a mind', then you would presume that it had a mind. Of
course, there's always the initial possibility that you are listening to a tape recording, but if you
manage to continue an intelligent conversation, that can be ruled out. Then there's the possibility that
your 'alien' is merely a mechanical probe responding to instructions from real aliens in their orbiting
space ship or back on Mars, and relaying their questions to you. In that case, you are dealing with
real minds, at one remove.

However, that misses the real point of the question. With an alien being, we lack all sorts of basic
evidential cues. We can't tell the difference between a 'smile' and a 'frown', or between different tones
of voice. There's little to empathize with. Or we might be faced with the more extreme Star Trek
scenario of a being made of pulses of incandescent energy. Does that pose an insuperable problem?

The mathematician Alan Turing proposed a famous test which could be used to determine whether
an individual at the other end of a computer terminal had a mind. The test is to see whether you can
keep up an intelligent conversation. In other words, there's sufficient evidence going by speech alone
to make a decision. Going by that test, it is irrelevant how physically different the alien is from us.

For anyone who has doubts about the sufficiency of the Turing test - as I have - the question remains
open. Suppose that someone suggested that the aliens were intelligent, but unfeeling machines.So it
was morally acceptable to use the aliens as tools, enslave them, put them to whatever purpose we
liked. The question is whether there is a philosophical argument to show why that attitude would be
wrong.

Geoffrey Klempner