  But what has not changed — and what is important for our  purposes — is that in every version of the grammar of (say)  English, the rules governing the syntactic structure of sentences and phrases are stated in terms of syntactic categories that are highly  abstracted from the properties of utterances that are accessible to  experience. As an example of this, consider the notion of a  trace. Traces are symbols that appear in phrasemarkers and  mark the path of an element as it is moved from one position to  another at various stages of a sentence's derivation, as in (1),  where ti markes the NP Jacob's position at an  earlier stage in the derivation.