Final answer:
The first syntactic criterion to determine whether a word is a verb or not is its ability to express an action or state.
Step-by-step explanation:
The first syntactic criterion to determine whether a word is a verb or not is its ability to express an action or state. Verbs are defined as action words, but may also introduce states or descriptions. They are often marked by auxiliaries (will, shall). Many verbs require an object (who or what is receiving the action).