Fowler's says both are acceptable. "Dreamed" is used more for emphasis and poetically. "Dreamt" is more common in British English but no definitive rule applies.
I would say 'Jill made cakes while Jack dreamed he was a pilot'. But I would say 'Jack dreamt he was a pilot' if I was just referring to some instance in the past.
I think it depends on context rather than tense.
'Last night I dreamt I went to Manderley again.'
but
'I dreamed a dream of time gone by'.
'I dreamt a dream' sounds a bit clunky.
Yes, tense is probably not right at all. But what I meant was if I explaining a situation that the reader was to understand and be transported to for the moment, as happens in a novel say.
A friend of mine is writing a children's book, first attempt, about a little boy who had dreams about adventures he took his friends on and so the chapters start off as 'Jack dreamed he was a ....... and I just thought it would sound better as dreamt and so that is why I asked.
Thanks for your answers.
either's okay in my book. The exception seems to be "learned", which now seems to have become an adjective to describe someone with a lot of education, so I always say learnt for the verb.
If anyone asks you to give two words ending in -amt, the other one's undreamt.