Null morphemes are theorized to be those morpheme strings which, while possessing no identifying characteristics, nonetheless allow us to differentiate between different forms of a word. Morphologists propose various theories for how these null morphemes may exist and whether or not we learn them naturally as part of the process of language acquisition.

An allomorph occurs when a morpheme varies in pronunciation but not in meaning. For example, the pluralizing morpheme "s/es" in English sounds like "z" in bubbles, but like "s" in cats. Recognition of these allomorphs is often much more difficult for non-native speakers of a language.

An allomorph occurs when a morpheme varies in pronunciation but not in meaning. For example, the pluralizing morpheme "ed" sounds like a "schwa" in wasted but like "t" in wished.

Derivational morphemes change either the semantic meaning or the part of speech to which the base word belongs. For example, in the word atypical the derivational morpheme a- reverses the meaning of the word typical to mean "not typical". The usage of the morpheme -er to change "wise" to "wiser", on the other hand, is inflectional only, as it only changes the comparative state of the associated adjective wise.

Inflectional morphemes are morphemes which modify either a noun/pronoun/adjective's number, gender, or case, or a verb's tense, mood, number, person or aspect, but do not chance the word's overall meaning or the part of speech to which the word belongs. The morpheme -ty at the end of the word cruel changes the word from an adjective to a noun, and is thus an example of a derivational morpheme.

Non-fluent aphasia, such as Broca's aphasia, is often triggered by damage due to stroke or other cardiovascular problem, and often produces the short, morpheme-absent language typical of telegraphic speech.

The answer makes more sense when you realize that the past tense and past participle of the verb wait are both waited. Consider the sentences "I waited for John for half an hour" and "I had waited for John for half an hour" -- both grammatically correct, but implying different things about the present.

Phonemes are the basic units of sound that distinguish one word from another in a particular language. The number of phonemes the human mouth and vocal cords can produce is limited by physiology. Within this limit, an extremely high number of morphemes can be produced.

Some languages, such as Arabic, benefit from having their phonemes developed at nearly the same time as their alphabet, so that each letter directly or almost directly corresponds to the sound it makes in the language. English uses a slightly modified form of the Latin alphabet, originally designed with Latin phonemes in mind, and thus poorly represents its 26 letters phonemically. This causes great difficulty for speakers of more phonetically aligned languages.

Semantics refers to the fact that children must learn combinations of phonemes that represent certain events, people, or objects. Pragmatics refers to the usage of different words, phrases, and slang terms. Children must learn how tone of voice and modulation can shape the meaning of a sentence. The same sentence might mean two different things in different contexts.