A Developmental Perspective on Language Acquisition 31facilitate language comprehension. For example, during the song,
“If You’re Happy and You Know It,” the caregiver claps the baby’s
feet or hands together as the relevant word is sung.
At around the time of their first birthday, infants make the
transition to language usually producing their first meaningful
word. Typically developing one-year-olds might understand
about 80 different words whereas they produce only about ten
(Pence Turnbull and Justice 2017). The so-called One-Word
Stage, which lasts from about 12 to 18 months, is characterized
by a slow start and later increased rate of word acquisition.
During this time period, many toddlers acquire approximately
50 different words in their expressive vocabularies that can be
categorized in different ways. At this stage typically developing
children understand many more words than they produce. A
comprehension strategy they might use at this stage is to look at
the object mentioned by the adult (Miller and Paul 1995).
A traditional description of the words children learn to say and
understand classifies them according to various word types such
as nouns, verbs, and adjectives. Using this taxonomy, first words
include nouns such as “car,” verbs such as “go,” and adjectives such
as “hot.” In a broader descriptive system, nouns, main verbs, and
adjectives are considered “content” words because used alone they
can convey meaning. These content words contrast with “function”
words which include copula and auxiliary verbs such as “is” and
“are,” prepositions such as “in,” and conjunctions such as “and.”
These words that have a primarily grammatical function rarely
appear at the earliest stages of language development. Bloom and
Lahey (1978) classified early words with another broad system.
They divided first words into two categories, namely substantive
words, which are primarily nouns, and relational words, which
include verbs and adjectives among other word forms. According
to this system, young children combine substantive words with
relational words once they begin to put together words in the