In linguistics, the head directionality parameter is a proposed parameter that classifies word order accordingly to the placement of the head stem, which can be either:
This assumes the language has a fixed word order in that part of its grammar to begin with. English and Romance languages are often given as examples of head-first languages, whereas Japanese and Basque are often given as examples of head-last languages, meaning that these languages have a consistent word order across all areas of their grammar. For example, English, German, and Japanese each construct subordinate clauses (with verbs as their heads) in different ways:
However, this simple dichotomy runs into two problems when used to classify entire languages in this way: Many languages, even considering only those with relatively fixed word orders, are not consistently either head initial or final across different areas of their grammar; and it is difficult find a definition of 'head' that is consistent across these different areas. For instance, either the subject or the verb may be considered the 'head' of the clause, yielding results as to which languages are considered head initial, or whether word order is consistent between, say, clauses and noun phrases, that are theory dependent rather than descriptive.