The utterances children hear aren't just lists of bare words strung together. Rather, speakers generally modulate their words in ways that add further information about the specific meaning being conveyed. These modulations take the form of inflections, usually suffixes, added to word-stems, and of freestanding grammatical forms like articles and prepositions. Some languages indicate which role is being played by the referent of each noun phrase (e.g., agent, recipient, place, instrument); they do this through word-endings, case markings, added to the noun. They mark the doer of the action with nominative case, or where the event took place with locative case. On verbs, they can mark when an action took place with tense marking on the verb, or the general temporal “shape” of an action – whether it was completed, reiterated, or lasted for some time – with an aspectual ending on the verb, and so on. They may also mark gender on nouns (e.g., masculine, feminine, neuter) as well as on the articles, adjectives, and sometimes the verbs that go with those nouns. And they may mark person (e.g., first, second, or third person on the verb) and number (e.g., singular or plural on nouns, verbs, and adjectives). That is, many languages show which elements belong together in a noun phrase, in a predicate phrase, or in a prepositional phrase.
Languages modulate nouns and verbs with inflections, but they differ in how much added information is provided this way, the regularity of the affixes used, and the division of labor between reliance on added grammatical elements (both inflections and free grammatical morphemes) and reliance on word order.
Inflections and typology
Languages differ a great deal in how they manage these modulations. Typologically, some languages are analytic (with little inflectional morphology, as in Mandarin Chinese); some synthetic (with extensive reliance on inflections that mark several distinctions simultaneously, as in Spanish or Hebrew); and some agglutinative (with highly regular inflections, each marking a separate distinction, as in Turkish or Hungarian). In analytic languages, a specific distinction may be unpacked, so to speak, so the notion of first-person plural, expressed in English by the pronoun we, may be conveyed by a combination of a first-person form plus a plural marker, as in Mandarin wo3.men2 (first-person + plural, or [1p + pl]). English is more analytic than synthetic, but like many languages, it presents a mixed picture.