an hypothesis? I am not a native speaker (and not very language talented) so I would appreciate any explanation/rules.
In US usage, words beginning with a silent h take an as if they began with a vowel
Words that begin with h in an accented or stressed syllable take a
Words that begin with h in an unaccented (unstressed) syllable can take either
an historic occasion
a historic occasion
In the first version, following an, the h is often effectively silent, but both pronunciations are heard.
The use of a in this last case is much more common, and the use of an may be viewed by some as a bit pompous, but surely correct.
‘H’ represents a consonant sound, so we would expect ‘a hypothesis’, and that is what many say and write. However, where the stress in a word beginning with a sounded /h/ is on the second or subsequent syllable, some native speakers precede the word with ‘an’ rather than ‘a’, so you will also see and hear ‘an hypothesis’. But if you say and write ‘a hypothesis’, you will not be wrong.