Syntactics, or syntax, is concerned with the way sentences are constructed from smaller parts, such as words and phrases. Two steps can be distinguished in the study of syntactics. The first step is to identify different types of units in the stream of speech and writing. In natural languages, such units include sentences, phrases, and words. In artificial languages, lexemes, tokens, and formulas are usually found among the basic units. The second step is to analyse how these units build up larger patterns, and in particular to find general rules that govern the construction of sentences.