First, the technical jargon: Every complete sentence contains two elements: a subject and a predicate. The predicate is a verb or a verb phrase. Run is a verb; run well is a verb phrase, where well describes how the person runs. The subject is a noun or pronoun (Dave is a noun; he is a pronoun) or a noun phrase that describes who or what did the action. Dave can be the subject, or people who are living can be the subject; the second one is a “noun phrase,” where noun people is further described by the information that they’re living.
Now, let’s simplify: a complete sentence requires a subject and a verb.
A verb, of course, is an “action word,” a word that does something, such as drink or eat or walk or sleep. These words all describe action; they are verbs. The subject is the person or thing doing the action. Here is a simple sentence which contains nothing but a predicate:
That, believe it or not, is a complete sentence, even though it contains only two words. The second word, ate, is a verb; it describes an action. The first word, John, is the subject; it tells us who did the action. It is important to understand that no sentence is complete until it contains both a subject and a verb. A sentence that does not contain both is called an “incomplete sentence.” Here is an example:
This is where people get confused, because running is a verb (more or less). We needn’t get into the technicalities of what the word running is called in this use; the important thing is to recognize that running here is merely telling us which people, it does not tell us what the running people are doing while they’re running.
The easiest way to make that phrase into a complete sentence is to add a form of the verb to be: is, are, were, etc. So we make that a complete sentence thus:
The people are running.
Or we can use “people running” as a noun phrase, describing which people form our subject. This will require that we add a verb or predicate to the phrase to create a complete sentence:
The people running are late.
You will notice that both sentences use are as the verb, and are as we already mentioned is a form of the verb to be. And we can change the noun phrase people running into a simple noun (people) simply by moving the verb to a different position:
The people are running late.
Finally, the simplest form of a sentence contains just a subject (noun or pronoun) and a verb. (I am not addressing imperative sentences here, which are commands such as “Go!” We’ll do that some other day.) This brings us to the name of God:
Remember the basic rule: a complete sentence requires a subject and a verb.