Active voice  -  The active voice means that the sentence does not use variations on the "be" verb as its main verb phrase. "He cut the tree down" is active, while "the tree was cut down by him" is not active but passive.

Aphasia  -  An aphasia is a deficit in a person's ability to understand or produce coherent and grammatical speech. Specific types of aphasia, such as Broca's aphasia and Wernicke's aphasia, cause deficits in specific linguistic abilities.

Categorical Perception  -  The tendency to perceive phonemes as members of only one category. We can produce sounds that are somewhat like [ch] and somewhat like [sh], but we will perceive them as only one or the other.

Function Word  -  Function words, like "that," "who," or "the," help us parse sentences by giving clues to the grammatical roles of content words.

Garden-Path Error  -  Garden-path errors occur when, while reading a sentence, some rule usually used in parsing is violated, forcing the reader to reinterpret the sentence and try to parse it in a new way.

Irregular Word Forms  -  An irregular verb or noun does not follow the same rules for modification as most other verbs or nouns. For example, most verbs are changed to past tense by adding the suffix "-ed"; "went," "broke," and "sat" all violate this rule, and are therefore irregular.

Linguistic Universal  -  A rule of syntax that holds true in many different languages.

Morpheme  -  A unit of language that has some innate meaning. Words, such as "run" and "boy" are content morphemes; while the ending "-s," which signifies a plural, and "- ed," which signifies the past tense, are function morphemes.

Overregulation  -  Children around age three or four tend to apply rules of syntax to every word they encounter, leading to incorrect forms of irregular words, such as "goed" instead of "went," and "gooses" instead of "geese."

Parse  -  Parsing a sentence is the process of figuring out each word's role in the syntax of a sentence. Is the word a noun or a verb? Is it a subject or an object? What function does it play in the phrase?

Passive Voice  -  The passive voice means that a sentence uses some variation on the "be" verb as its main verb phrase. "The tree was cut down by her" is passive, while "she cut the tree down" is not passive but active.

Phoneme  -  A unit of sound that is used in spoken language. Each letter of the alphabet represents one or more phonemes, such as [b] and [t], and there are also combination phonemes, like [ch] and [sh].

Phrase  -  A phrase is a unit of a sentence that serves some syntactical function. For example, a normal sentence might have a noun phrase, a verb phrase, and an object phrase.

Phrase Boundary  -  The point of separation between two adjacent phrases in a sentence. In the sentence "The boy kicked the ball," the phrase boundaries would lie between "boy" and "kicked" and between "kicked" and "the."

Speech Segmentation  -  The process by which humans divide auditory input into distinct phonemes and words. There are no spaces of silence or breaks between phonemes or words, but we perceive them as distinct entities nonetheless.

Syntax  -  The term syntax encompasses all the rules of sentence structure that determine how we interpret and understand phrases and sentences in a particular language.