The relation between intelligence and language is complex. If intelligence is defined as the ability to solve problems, generate creative ideas, recognize emergent categories and patterns, or simply as processing power or speed of neural conduction, then language can be viewed as a secondary process in that it merely serves to communicate the workings of the intelligent mind. This language-independent conceptualization of intelligence can be contrasted with a language-dependent perspective, in which verbal skill per se is an integral aspect of intelligence. From the language-dependent perspective, intelligence includes abilities such as knowledge of word meanings, mastery of grammar and syntax, and skilled articulation of ideas.

Verbal and nonverbal skills co-occur in normal adults, and efforts to separate them are problematic: Most verbal tasks tap underlying nonverbal skills, and tasks that seem nonverbal may be influenced by verbal mediation of instructions or ongoing processes. However, from a developmental perspective, separating verbal and nonverbal skills is obvious and necessary. In the first year, most human infants begin to babble, use gestures, and understand and say a few words, but these activities pale in comparison to the infant's interest in object manipulation, locomotion, and visual exploration. Our terminology for the first year of life evokes this relative lack of language – the word infant is from the Latin infans, meaning “incapable of speech.” Infants do communicate, but their linguistic investment seems relatively minor in comparison to their other abilities and to the prodigious advances in language that characterize the second year.