An Australian correspondent writes to say that he's encountered sentences like I have been to the cinema yesterday which, he says, would be 'completely out in British English'. It seems like a natural development, he adds, but asks: 'isn't this against the "rules" of simplicity, which languages are so keen to comply with? Isn't it more "economical" to use simple structures than complex ones and aren't languages prone to such economy?'
I don't think economy has anything to do with it. Simplicity is only one factor in promoting language change, and is not always the determining factor. Issues of identity and clarity, for example, can motivate the maintenance of a more complex construction.
'Completely out' in British English? Not so. I use this kind of construction regularly. All that has happened is that the aspect has shifted, which is perfectly normal in spontaneous speech. At the beginning of the sentence, the notion of current relevance is in the forefront of the speaker's mind; at the end of the sentence, it isn't, thus allowing the use of such adverbs as yesterday. One can even renew the current relevance meaning, as in a response to Have you been in touch with John about what he owes me? It could begin: Yes, I've spoken to John yesterday, and ... Now, what will come next? I've told him what you said or I told him what you said? It all depends on whether the have spoken bit is in the forefront of our mind (in which case we'll probably stay with the present perfect) or whether the yesterday bit is (in which case we'll probably switch to past).
All this is for spontaneous colloquial speech, of course, where sudden changes of thought are normal, but I think people are more likely to follow the traditional constraint in formal speech and in writing. I would myself. But even in everyday speech a lot depends on the semantics of the adverbial.
I've seen him yesterday.
I've seen him a day ago.
I've seen him a week ago.
I've seen him six months ago.
I've seen him last year.
I've seen him 10 years ago.
For me, these are increasingly unacceptable because increasing strain is being placed on the notion of current relevance.
The system does seem to be slowly changing. Or perhaps I should say 'reverting', for there are examples of ago with a present perfect in Middle English -in Chaucer, for instance. And there's probably some pressure coming from the modal construction (I should have done it yesterday).