I mentioned the Subject of a Sentence and the Predicate earlier in the page about the Parts of a Sentence. I had said there that the division of a sentence into these two parts was based on meaning. To refresh your memory about Subject and Predicate, click here.
There I had promised to give you a more detailed explanation...and this is what I am going to do now. I am going to explain...
When we talk of the subject of a sentence in grammar, we mean a particular part of the sentence. This part has certain special properties and behaves in a particular way in the sentence. We can also call it the grammatical subject.
In all these sentences, the italicized part is the subject and the remaining words (ride bikes) is the predicate.
The subject may be one word or more.
In sentences 1 and 5 above, we have one-word subjects. in others, we have more than a word.
The groups of words (as well as the single words in sentences 1, and 5) in italics are called phrases.
In sentences 1-4, the main word is a noun (boys). In the last sentence, it is a pronoun (They). This main word is usually called the head word of the phrase. Any phrase that has a noun or pronoun as its head word is called a noun phrase.
Even if you have the head word alone, noun or pronoun, as in sentences 1 and 5, that word is called a noun phrase in modern grammar.
The whole subject can be replaced by a pronoun.
The pronoun 'they' in sentence 5 is a perfect replacement for the noun phrases in the previous sentences.
The head word of the subject can be modified.
Adjectives, adverbs, and determiners can modify the head word of the subject.
The words: smart (adjective), very (adverb), and some (determiner), illustrate this idea.
The head word will always be in the nominative case.
The head word in the first four sentences cannot be boys', i.e. with an apostrophe (genitive case); it has to be boys, i.e. nominative case.
In sentence 5, the head word has to be the word they; it cannot be them or theirs or their.
Words such as boys and they are said to have the nominative case form. Refresh your memory about grammatical case here.
About the word 'boys' in sentences 1 to 4, we have the following information:
We have almost the same information about the word 'they' in sentence 5.
Semantically, the subject of a sentence may be an agent or a patient.
If the verb is an active verb, it shows that the subject is an agent (i.e. someone who does an action - a doer). In our examples, the verb 'ride' is an active verb. Therefore, the subject 'boys' and 'they' are agents.
The subject could be a patient (one who suffers an action, good or bad) in another sentence. This happens if the verb is a passive verb.
Look at the sentence: "The workmen were praised by the boss."
Here, the verb 'were praised' is in passive form; and therefore, the subject head word 'workmen' is a patient.