Final answer:
The fourth syntactic indicator to determine whether a word is a noun or not is sentence position.
Step-by-step explanation:
The fourth syntactic indicator to determine whether a word is a noun or not is sentence position. The position of a word within a sentence can often indicate its grammatical function. For example, in the sentence 'I saw a dog,' the word 'dog' is in the position of the object, indicating that it functions as a noun.