I’d like to look at a sentence which caused some difficulty for a student of mine lately. It involves the word that, or really I should say it involves its absence. We often omit words in our speech and writing to establish a more natural tone, but in analyzing a sentence, we have to restore what has been left out in order to understand how the sentence works and sometimes make it better.
Here’s the sentence: The climate of those northern islands is nearly of the tropical latitudes now. The first step always in analyzing a sentence is to determine the number of clauses it comprises. Here there is just one clause, with the subject phrase being the climate of those northern islands and the balance of the sentence, beginning with the verb is, making up the predicate. Compositionally, then, we have a simple sentence, but grammatically it’s not so simple.
The difficulty lies with the verb is. This word is one form of the verb to be, and the verb to be can be used in three ways: to mean exist, to mean exist as, and to act as an auxiliary to another verb. If I say that the car is in the garage, I mean to communicate the fact that the car exists there, and since there is no direct object in the predicate, only an adverbial phrase, we classify this use of to be as an intransitive verb. If I go on to tell you that the car is a sedan or is old, I am not telling you that it exists, but that it exists as something; in the first case I am identifying the subject car with a noun, sedan, and in the second case I’m identifying the car with an adjective, the quality old. When the verb to be identifies a subject with a noun or pronoun or adjective in the predicate, we classify it as a copula, or linking verb. Finally, if I say that the car is holding up well, the verb is helps form the progressive aspect of the verb hold up, meaning to last or endure. In this third use, the verb is does not stand as the principal verb of the clause, but as an auxiliary, something used to construct a particular tense and form of another verb.
In our analysis, we can rule out this last function of an auxiliary verb, because there is no other verb than is in the predicate; it must be, therefore, not an auxiliary verb but the principal verb itself. So the next question to decide is whether the verb is as the principal verb is functioning here as an intransitive or as a copulative; in other words, does it mean to say simply that the climate of those northern islands exists in a certain way, or does it mean to say that we should identify that northern climate with another, namely, a tropical climate? If we look closely at the predicate, the words nearly of the tropical latitudes now intend to describe the subject, the climate of those northern islands. To describe something requires an adjective, and we can in fact regard the prepositional phrase of the tropical latitudes as an adjective. This will rule out the possibility that the verb is functioning here as an intransitive verb, but it also leaves us with an awkward identification of the subject with something else in the predicate: just what is an of the tropical latitudes?
What’s missing, then, is a noun or pronoun in the predicate which identifies the subject clearly with something else. So if we add, for example, the demonstrative pronoun that, things begin to clear up nicely: The climate of those northern islands is nearly that of the tropical latitudes now. We have now a distinct identification between two things, climate = that, with the pronoun that then modified by the adjective phrase of the tropical latitudes. This addition of what is called a predicate pronoun makes it clear that the verb is stands in this sentence as a copula, and helps the writer make an explicit comparison of two things, noun and pronoun, rather than the more difficult comparison of noun and adjective phrase alone.
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