We could easily settle the question of whether there is a Universal Grammar (Chomsky) and whether there is a Language Instinct (Pinker) - the latter being the idea that language in Homo sapiens should be viewed as a unique biological adaption of our species, like the Elephant's trunk.

No other species on this planet has trunks and no other species has language.

All we need to do is to capture an extra-terrestrial and see how his/her/its language works, and whether it shares the same broad grammatical categories and functions of human languages.

Either the extra-terrestrial language will be similar to human languages, or it will be significantly different.

If it is significantly different then this supports the notion that human language is a species specific adaption (like the elephant's trunk).

If similarities are discovered, then this will either be a total fluke, or, more pausibly, it will reflect the fact that for an organism to survive in a hostile environment certain features of language are necessarily present (adaptively useful) in any organism with a brain capable of language.

Great idea but to recognise a significantly non-human language in any way other than how it's transmitted (e.g. clicking sounds or poop-stains in intricate patterns), we'd have to be pretty smart.

We'll (hopefully) know soon enough if the research on dolphin communication hurries along though!

Actually we might not need to capture an ET, because, if their reports are to be believed, lots of people have already contacted ETs who spoke good English.

Miland:Actually we might not need to capture an ET, because, if their reports are to be believed, lots of people have already contacted ETs who spoke good English.

I am impressed by your command of the historical documents.

Above all, we must define what is meant by language: what criteria are relevant: communication, phonetic articulation or syntax?

After that, one can elaborate tests to decide wheter some other (extra)terrestrial species uses some language.