Syntax is the discipline that examines the rules of a language that dictate how the various parts of sentences go together. While morphology looks at how the smallest linguistic unit (called morphemes) are formed into complete words, syntax looks at how those words are formed into complete sentences.

Syntax is not prescriptivist – which is to say, it does not attempt to tell people what the objectively correct way to form a sentence is. Rather, it is descriptivist, in that it looks at how language is actually used and tries to come up with rules that successfully describe what various language communities consider to be grammatical or non-grammatical. Syntax deals with a number of things, all of which help to facilitate being understood and understanding language. Without rules of syntax, there would be no foundation from which to try to discern meaning from a bunch of words strung together, whereas with syntax, an infinite number of sentences are possible using a fairly small finite number of rules.

One part of syntax, called inflection, deals with how the end of a word might change to tell a listener or reader something about the role that word is playing. Regular verbs in English, for example, change their ending based on the tense the verb is representing in a sentence, so that when we see Robert danced, we know the sentence is in the past tense, and when we see Robert is dancing, we know it is not. As another example, regular nouns in English become plural simply by adding an s to the end. Cues like these play a large role in helping hearers to understand sentences.

Another part of syntax covers the various parts of speech that a language uses and separates the words of the language into these groups. Each part of speech in turn has various rules that may be applied to it, and other rules that dictate when it can’t be used. English, for example, makes use of nouns, verbs, adjectives, articles, pronouns, prepositions, adverbs, and others, while other languages may not have a separate class for adjectives or may make use of classes not found in English.

Perhaps the most important aspect of syntax is how the various parts of speech connect together. Every language has rules that dictate where a part of speech is allowed and where it is not, and how to interpret the resulting sentence. For example, in English, our basic order is Subject Verb Object; this means that in a simple sentence, the first noun phrase is the subject, and the subsequent verb phrase may contain the object. This allows us to deduce that in the sentence The boy kicked the ball, the boy is the subject, and therefore the one doing the kicking, whereas the ball is the object, and therefore being kicked. If the sentence were The ball kicked the boy, the meaning would be reversed somewhat confusingly, and if it were Kicked the ball the boy, we would immediately recognize it as violating our basic syntactical order and therefore as being ungrammatical.