Phonetic Form and Logical Form

A foundational distinction in syntax separates two levels of a sentence. Phonetic form (sometimes phonological form) is the form that morphemes take when pronounced. Logical form is the order in which the morphemes are interpreted. Keeping these apart lets the theory account for cases where what we hear and what we understand come apart.

This distinction has driven a great deal of syntactic work. It is closely related to what used to be called surface structure and deep structure, with deep structure corresponding roughly to logical form and surface structure to phonetic form. Phonetic form and logical form are the terms used today, but the core idea is the same: in any given sentence there may be a mismatch between how the sentence is pronounced and how it is interpreted, and the theory has to separate the two.

An ambiguous sentence

Consider the sentence every boy hugged a girl. How many girls are there? The sentence is genuinely ambiguous. On one reading, every boy hugged a single, particular girl, so there is only one girl. On another reading, every boy hugged some girl or other, so there could be three girls — one per boy — with each boy hugging at least one.

This is an empirical fact, not a matter of opinion: native speakers of English can and do understand the sentence in both of these distinct ways. It is equally a fact that both readings are pronounced in exactly the same way, every boy hugged a girl. So at some level the two interpretations must be separated from the single spoken form. The order we hear on the surface is not always the order in which the morphemes are interpreted.

Interpretation is not on the surface

The lesson is that interpretation is not equivalent to phonetic form, and interpretation is not always visible or audible. If the sentence itself does not settle which reading is intended, what does? The key is context. Is there some salient girl already in the context that leads us to read a girl as one specific individual? Or do we already know that several girls are involved?

Context, not the sentence in isolation, is what disambiguates. The sentence supplies one surface form; some other mechanism lets the hearer recover the meaning the speaker intended. The general point is that interpretation is not always plain and on the surface, which is exactly why phonetic form and logical form must be treated as separate levels.