Morphology is the study of morphemes. more A morpheme can be a bound morpheme (cf. affix) or a free morpheme, which is a morpheme that can stand on its own as a word. Morphemes are added to lexemes to make changes in tense, voice, mood, etc. Take the word “unbreakable”:
“un-“, a bound morpheme;
“break“, a free morpheme; and
“-able“, a bound morpheme.
Phonemes are letters; morphemes are parts of a word; and lexemes are words.