Bound morphemes cannot form words by themselves, they are identified only as component segmental parts of words. Free morphemes can build up words by themselves.
Example:
handful
the root hand is a free morpheme
the suffix -ful is a bound morpheme.
There are very few productive bound morphemes in the morphological system of English. Most of them are homonymous:
1) the morpheme -(e)s [-z, -s, -iz]: the plural of nouns, the possessive case of nouns, the third person singular present of verbs;
2) the morpheme -(e)d [-d, -t, -id]: the past and past participle of verbs;
3) the morpheme -ing: the gerund and present participle;
4) the the morphemes -er, -est: the comparative and superlative degrees of adjectives and adverbs.
The auxiliary word-morphemes do, be, have, will, shall, would, should, adverbial elements more, most, the infinitive particle to, articles can be called ‘semi-bound’ (полусвязанные) morphemes, since, being used as separate elements of speech strings, they form categorial unities with their notional stem-words.
II) according to formal presentation (формальная представленность)