Grammatical form and meaning

main verb phrase (MVP) - the main verb of a clause plus its auxiliary or helping verbs in an unchanging order.

As we will discuss throughout Analyzing Grammar in Context, whether a FORM is defined at the WORD level, the PHRASE level, or the CLAUSE level, we have formal tests for determining FORM and functional tests for determining FUNCTION. In most cases, FORMS will only take one of the four FUNCTIONS listed above. There are a few notable exceptions to this rule (structure-class words and independent clauses, for example); in other words, while the form and function of a form-class word is normally the same (noun functions nominally, for example), form-class words can also function differently from their form. In other words, a noun may function adjectivally, like BASEBALL BAT or TENNIS SHOES. On the other hand, the Form and Function of a structure-class word is always the same. For example, a determiner can only function as a determiner; a preposition can only function as a preposition, and we will cover these explicitly in Sections 4-6. Moreover, we will describe how some FORMS can only FUNCTION in certain ways, while other FORMS can FUNCTION in multiple ways. 
To summarize, we analyze for FORM (name something), but, more importantly, we also analyze to determine how a FORM is FUNCTIONING in a particular context. 
While these definitions apply to simple English sentences, defining the subject is more difficult in more complex sentences, and in languages other than English. For example, in the sentence It is difficult to learn French, the subject seems to be the word it, and yet arguably^{[according to whom?]} the real subject (the thing that is difficult) is to learn French. A sentence such as It was John who broke the window is more complex still. Sentences beginning with a locative phrase, such as There is a problem, isn't there?, in which the tag question isn't there? seems to imply that the subject is the adverb there, also create difficulties for the definition of subject.^[1]
In languages such as Latin and German the subject of a verb has a form which is known as the nominative case: for example, the form 'he' (not 'him' or 'his') is used in sentences such as he ran, he broke the window, he is a teacher, he was hit by a car. But there are some languages such as Basque or Greenlandic, in which the form of a noun or pronoun when the verb is intransitive (he ran) is different from when the verb is transitive (he broke the window). In these languages, which are known as ergative languages, the concept of subject may not apply at all.
The subject (glossing abbreviations: sub or su) is, according to a tradition that can be traced back to Aristotle (and that is associated with phrase structure grammars), one of the two main constituents of a clause, the other constituent being the predicate, whereby the predicate says something about the subject.^[2][3] According to a tradition associated with predicate logic and dependency grammars, the subject is the most prominent overt argument of the predicate. By this position all languages with arguments have subjects, though there is no way to define this consistently for all languages.^[4] Even in languages such as English, there is not always a perfect match between the semantic predicand and the subject, as a predicate may be predicated on an argument in another clause (see raising).
From a functional perspective, a subject is a phrase that conflates nominative case with the topic. Many languages (such as those with ergative or Austronesian alignment) do not do this, and by this definition would not have subjects.
All of these positions see the subject in English determining person and number agreement on the finite verb, as exemplified by the difference in verb forms between he eats and they eat. The stereotypical subject immediately precedes the finite verb in declarative sentences in English and represents an agent or a theme. The subject is often a multi-word constituent and should be distinguished from parts of speech, which, roughly, classify words within constituents.
In the example sentences below, the subjects are indicated in boldface.

1.