Movement

The last of the key structural terms is movement. Movement occurs when a morpheme changes location in a sentence. Some find the idea suspicious — why should words move around at all? — but that is exactly what the term names. Movement is constrained: a head moves to a head position, and a phrase moves to a phrase position.

Heads to heads, phrases to phrases

One common instance is a verb moving to the complementizer position, known as V-to-C movement. The constraint is that a head moves only to another head position, so a verb does not move into a complementizer phrase position; rather, a whole verb phrase could move to a complementizer phrase position while a bare verb moves to another head. The general principle is simple: heads move to heads and phrases move to phrases.

Movement and meaning

The interesting question is why movement happens and whether it is constrained. Consider Ezra is giving his stuffed animal to a child. Move the auxiliary is to the front and the result is Is Ezra giving his stuffed animal to a child? — suddenly the sentence is interpreted as a question. Why should moving the auxiliary to the front turn a statement into a question? Speakers do this intuitively, without reflection.

The pattern is not confined to English. In language after language, question words tend to appear near the beginning of the sentence. That so many unrelated languages do something so similar is itself remarkable, and it deepens the puzzle of why this movement occurs. Whatever the ultimate explanation, the empirical generalization is clear: movement is often a signal to interpret something differently. When movement occurs, a difference in interpretation typically comes with it — syntactic movement is being used to encode meaning.

Compositionality again

This is where compositionality becomes central. Ezra is giving his stuffed animal to a child and Is Ezra giving his stuffed animal to a child? contain exactly the same words. Yet once the order changes, the morphemes are interpreted differently, and the whole expression means something new. Even though every individual component is identical, the complex expression differs because the parts have combined differently. This is one clear, simple illustration of how syntax affects meaning.