So I'm trying to figure out how to provide proof that something is a subject of a sentence. I know to prove something is a noun, you can put determiners in front of it, and pluralize it (if it's a count noun). For verbs, you can inflect it. For adjectives, you can scale it with modifiers like "very."

So what are two ways you can prove something is a subject of a sentence?

  • 1
    Just try proving something is the subject of this sentence! Commented Sep 30, 2015 at 17:41
  • I think the simplest way is to show that a subject can be replaced by he/she/it/they. I think this works in most cases. Perhaps there are cases where this does not work, but at the moment I can't think of any.
    – rogermue
    Commented Sep 30, 2015 at 18:12
  • The answers in that question linked above is all about "finding" the subject of a sentence. Good luck with trying to follow all the leads... :-)
    – Mari-Lou A
    Commented Sep 30, 2015 at 19:20
  • All you can do is show that the word can be validly interpreted as a noun and that some otherwise-valid parse of the sentence has it as the subject. But there are a great many cases where this is ambiguous. There is no "proof" in the general case.
    – Hot Licks
    Commented Sep 30, 2015 at 20:12

2 Answers 2


Absolute proof may be too high a bar. But you can gather persuasive evidence with word order, verb form, and semantics. Let's start with identifying those subjects that are noun phrases of clauses.

First determine whether you're dealing with an interrogatory. If so, transform the sentence to the declarative form:

Are you the one? -> You are the one.

Determine whether the verb is in the imperative mood. If so, the subject is you, the audience being commanded or exhorted, and you're done. You'll have to be familiar with relevant English idioms:

Let me help you.

For declarative sentences, determine the verb type.

  1. A copulative verb links or describes, and the noun linked to or described is the subject. That noun will not be governed by a construct taking an object, and it will either be the only noun or the closest noun preceding the verb.

The land beckoning John was a world unto itself.

As the object of the participle, John, isn't a candidate; land precedes the verb was, so it's linked to world and is the subject.

If all you've got is the one noun, its position won't matter. In

The land was beautiful

or the poetic

Beautiful was the land!

land is what's described and it's the subject in either case.

  1. An intransitive verb declares a state, and the subject is the noun in that state. Same positional rules as 1.

John lies in his bed.

  1. A transitive verb carries an action, and in the active voice, the subject performs the action.

John hit the wall with a hammer.

  1. A transitive verb in the passive voice will have a subject on which the action is performed.

The wall was hit with a hammer by John.

I haven't described how to determine the direction of the action, but you do that by word order and eliminating objects as candidates.

There are no doubt exceptions that don't conform to these steps.

And note that English is highly recursive, so this is only a start. Non-clause verb forms like infinitives and participles may have subjects, and both these verb forms and whole clauses may act as subjects of the clauses in which they're contained. But it is a start.


You can test using a transformation that is triggered by a subject.

Easiest and most usual is subject-verb agreement: most finite verbs agree in number with a third person subject. "loves" agrees with the subject in "John loves women", "Women love John". (Problematic are sentences with "there", like "There seem to be unicorns in the garden", where "seem" is apparently not agreeing with its subject "there".)

Subject-raising affects only subjects. "I believe the earth [subj] has a moon" => "I believe the earth [old subj is now object of believe] to have a moon".

Quantifier-float usually affects only subjects. "Each of the boys ate an apple" => "The boys ate an apple each". (Not "The boy ate each of the apples" => *"The boy ate the apples each".)

  • Exactly. "Subject" is defined by its uses, and those can mostly be teased out by transformations. Note, too, that all subjects are noun phrases, but not all noun phrases are subjects; the definitions and tests are different. Commented Oct 1, 2015 at 16:06

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