Considering that the subject can be a noun, pronoun, noun phrase, gerund, infinitive, or subordinating clause, it is important to understand where a subject is placed.
The subject of a simple sentence or a clause usually appears before the corresponding verb. For example,
It is also common for various phrases to appear between the subject and the verb. For example,
These intervening phrases usually do not modify the nature of the subject, especially its characteristics. You might be easily misled by the noun closer to the verb (in this case, “Solar System”), but care must be taken to identify the correct subject (“The Sun”).
Inversion is the grammatical word order in a sentence, phrase, or clause, where the normal word order pattern of subject + verb in English is reversed. In inversions, the subject takes the form of the auxiliary verb as either singular or plural but before the main verb. To explain further, the normal order is subject + auxiliary verb + main verb, with the auxiliary verb being optional. In our first example,
The sun (subject) + does (aux. verb) + raise (main verb) in the east.
In inversions, the order is auxiliary verb + subject + main verb.
While there are many different types of inversions, the most commonly known inversion is a question. For example,
In which direction does (aux. verb) the sun (subject) rise (main verb)?
Subordinate clauses can act as the subject of a sentence. A that-clause is the most common subordinate clause and begins a sentence or clause. A that-clause is also known as a declarative content clause. Science texts are replete with such that-clauses.
Relative clauses are another possibility. These are also tricky concepts in English grammar. A relative clause begins with a relative pronoun whose antecedent is (usually) the object of the previous clause. The challenging part comes when the object is a noun phrase with one or more prepositional phrases (in which case, the antecedent can be any of the nouns in the prepositional phrase) or when the relative pronoun indicates the entire previous clause (in which case, the subject is the entire previous clause). Here are some examples:
In subject phrases containing possessives, the head subject is the noun following the possessive.