Language is perhaps humans' greatest cognitive achievement. A complex system of word definitions and arrangements can effectively represent our entire inner and outer worlds. The language of poetry, novels, and plays evoke rich images and emotions, and the creative among us can generate whole other worlds using language. How do we produce and understand language?

Words are made up of features, basic units of production and perception. The auditory units of spoken language are called phonemes, while the units of written language are, of course, letters. We can modify words to tweak their meaning, such as by making nouns plural or verbs past tense. Finally, we produce a collection of words that adhere to strict rules of arrangement in order to make grammatically correct and understandable sentences. These processes are all based in the biological brain; infants and children show some innate language abilities, and the anatomy of the human brain reveals portions devoted to the production and comprehension of language. The study of language focuses on our shared understandings of the rules of language and on individuals' development of language skills over time.