What Does Simple Subject Mean. Simple subject definition: A simple subject is a main word or words that tell what or whom a sentence discusses, not including any modifiers. Simple subjects are subjects that have only one actor.
While I'm not suggesting that 'change' is a verb in 'subject to change', the fact that 'X is liable to change' does use a to-infinitive means that there needs to be some evidence given to support 'change is a noun here, not a verb'.
Sometimes, a simple subject does not perform an action, but instead is equated (or linked) to another noun phrase.
All though they both mean the subject they are two very different words. In its simplest sense, the subject refers to the doer of the action or to what (or whom) the sentence is all about. A simple predicate is almost like the simple subject.