English Semantics

In semantic analysis every proposition contains one predicate and a varying number of referring expressions (noun phrases) called arguments.The predicate may be a verb, an adjective, a preposition, or a noun phrase.
The arguments that accompany the predicate have different semantic functions, or roles, in the proposition. What roles they have depends partly on the nature of the predicate and partly on their own meanings.

The description of a sentence is a syntactic analysis. The description of a proposition is a semantic analysis. A syntactic analysis is an account of the lexemes and function words in a sentence, describing how these combine into phrases, and showing the functions that these lexemes and phrases have in the sentence. There are somewhat different ways of doing syntactic analysis, but generally these sentence functions are recognized: subject, predicate, object, complement and adverbial.
Note that every lexeme and function word is assigned to one of the syntactic functions, subject, predicate, etc., and these functions are listed in the order they have in the sentence.

The semantic analysis deals with meaning, the proposition expressed in the sentence, not necessarily with all the function words in the sentence. In semantic analysis we first separate Inflection from Proposition.

When Inflection—including Tense—is separated from Proposition, we see that the forms of the verb be (am, is, are, was, were) have no meaning. They are clearly part of the syntactic structure of sentences but not of the semantic structure.

An English sentence has certain kinds of modification that, together, we call inflection. Inflection includes tense (the distinction between present walk and past walked, for instance); aspect (are walking, have walked), and modality (may walk, could walk, should walk, among other possibilities). Tense, aspect and modality can be combined, as in were walking, should be walking, would have walked.

A proposition is something abstract but meaningful. It can be expressed in different sentences and in parts of sentences, perhaps with differences of focus but always with the same basic meaning.
And, as you recall, any sentence can be expressed in different utterances, produced by different people at different times and in different places.