[Beatrix]

which is correct? I've just encountered this question while writing a post. sorry if this sounds too elementary

I know it's correct to say "X lasts for centuries/years/weeks"

[susan53]

Both are fine. It's quite usual to drop the "for" when you're talking about a period of time and the verb itself expresses duration - eg : I've lived here for about a year or I've lived here about a year. It's only when the verb doesn't express duration that you need to make it explicit by using the pronoun. So : We stayed for half an hour or We stayed half an hour are both fine but only We went for half an hour. Because in fact it's not the act of "going" which lasted half an hour (and there's your example - last expresses duration so for is optional). The sentence implies "We went and then we stayed".
Hope that helps.

[Beatrix]

yes, everything is clear now, thanks a lot
I knew you would explain

[Beatrix]

but we still have to say it lasts for centuries, even though the verb to last expresses duration? is it taken for some fixed phrase then, or something like that?

[susan53]

No - it lasts centuries is fine. Try Googling it. And if you do a Google battle for the two phrases you'll find that it comes out as a 20/60 result. lasts for centuries is therefore more common, but there's no reason why the for can't be dropped. It's the same rule as above.

[Beatrix]

thank you very much!

[Beatrix]

susan, do you think I'm up to doing the CELTA course? since I have those questions...
do you perhaps have some grammar book to recommend?

the only one I have is Camridge Grammar of English by Ronald Carter and Michael McCarthy (very good though)

[susan53]

I think you'd be great on a CELTA course, and would get a lot out of it. The important thing isn't always knowing the answers but knowing which questions to ask. The answers come with experience, but if you never notice that there are questions to be asked, you never get the experience.

A book you might like is Scott Thornbury's About language (CUP).

[Beatrix]

thank you.