From what I remember to have learned in SPANISH, which is my mother tongue, affixes just refer to derivational morphemes such as suffixes and prefixes which can change the meaning of words when added to them. For example, agree - disagree (the opposite) or friend- friendly (from a person to a way of doing something).
However, the inflectional morphemes that mark grammatical functions such as tense or number are not usually considered affixes (and therefore suffixes) because they do not add meaning to the resulting word. It is the case of agree - agreed. We just call them inflectional morphemes, but not affixes.
IS THIS THE SAME IN ENGLISH? What I have seen so far is that most sources treat affixes as all prefixes and suffixes, either they are derivational or inflectional morphemes.
In any case, some sources actually specify that affixes are just the units added to a word changing their meaning, i.e. the derivational morphemes (what I think I learned in Spanish).
Which option is more accurate? Thanks in advance!