what is a clause?

A clause is a group of words with a subject and a predicate (verb part). If you don't see both of those things there, in a subject-verb relationship, then you're not looking at a clause. Clauses can be short or long. They can also be divided into all sorts of different categories, but we'll get to that later. Here are some basic examples, with the subject in blue and the verb in red.

Max had prodigiously torrential diarrhea.

Grimacing the entire time, Janet tentatively licked the bull's scrotum.

When you were young, you used to urinate whole sutras onto the carpet.

The following groups of words are not clauses:

Sitting naked on the branch, (no subject; verb in participial form)

a waste of perfectly good semen (no verb)

the last scheduled fart of the day (no verb; "scheduled" is an adjective)

Expertly strumming his penis, (no subject; verb in participial form)
After sniffing so many armpits, (no subject; verb in participial form)

hilariously overrated (no subject; no verb) 

A sentence with a compound subject and/or a compound predicate has only one clause.

Bill and Ted crawled into the cramped rocket. (compound subject)

Bill looked at pictures of Marlene and thought dirty thoughts. (compound predicate)

Bill and Ted saw Marlene and said "Whoa!" in unison. (compound subj.+ pred.)

A sentence with a single clause is called a simple sentence.

Compound and complex sentences, however, have more than one clause. Longer sentences can have as many as three or four clauses—sometimes even five. A compound sentence has two independent clauses. A complex sentence has an independent clause plus at least one dependent clause. A compound-complex sentence has two independent clauses and at least one dependent clause.

So before we go further, what are dependent and independent clauses?

An independent clause is a complete thought that can stand on its own.

Jimmy sneezed. Sarah farted sexily in response.

You can separate two independent clauses two ways to make compound sentences (more on this in a bit): (1) by using a semicolon or (2) by using a comma plus a coordinating conjunction such as the famous FANBOYS: for, and, nor, but, or, yet, so.

Jeremy was a sniveling weakling; the girls hated him.

Jeremy was a sniveling weakling, and the girls hated him.

Jeremy started lifting weights, but the girls still hated him. 

A dependent clause (also called a subordinate clause) is an incomplete thought. It cannot stand on its own. If you read such a clause, you expect to hear more—something that completes the thought.

If you flash me again,

When Connor arrived and saw the orgy,

After Gil the Glutton had eaten everyone's food,

You can see that the above are clauses because of the subject and verb. It should also be obvious that the above examples are not complete thoughts: they require something more to complete them. You also see that subordinate/dependent clauses are introduced by what's called subordinating conjunctions—words like before, after, when, if, unless, who, whom, what, that, though, although, as if, because, etc.

So here are two compound sentences (2 independent clauses):

Richard had earned the right to sit at the high table; he'd had to polish many knobs to gain such status.

Batman stepped warily amongst the writhing bodies covered in baby oil, but Robin was less cautious and seemed to be enjoying himself.

And here's a complex sentence (1 independent clause, 1 or more dependent): 

Richard had earned the right to sit at the high table because he had polished many knobs to gain such status.

Here's a compound-complex sentence (2 independent clauses, 1 or more dependent):

Richard had earned the right to sit at the high table because he had polished many knobs to gain such status; this is how he'd acquired the nickname Dick Lickler.

I'll talk about other ways to categorize clauses in another post, but for now, let's quiz your knowledge. By this point, you should be able to recognize whether something is a clause, tell whether a clause is dependent or independent, identify sentence types, and count clauses. Let's put you through a battery of quizzes and see how well you do.

QUIZ 1: Are these clauses?
Look at the groups of words below. Are they clauses or not?

1. After frying the egg,
2. When Janet realized what had happened to her dildo,
3. Clarence hated...
4. 1960s-era cars
5. ...after I wash my nethers.

QUIZ 2: Dependent or independent?

Look at the sentences below. Is the clause in boldface dependent or independent?

1. As per the tradition, when Kanta came of age, he would face the Ball-kicking Trial.
2. If you swallow it without vomiting, you'll earn my undying respect.
3. Marlon phoned his wife after he said goodbye to his adoring sheep.
4. Grant knew Lee was just over that hill because he could hear the distant farts of the Confederates.
5. Life's a piece of shit when you look at it.

QUIZ 3: What type of sentence?

Look at the sentences below. Is each respective sentence simple, compound, complex, or compound-complex?

1. When Albert Einstein was five, he saw his first naked woman.
2. When Einstein was five, he saw his babysitter having sex, and this led to his theories predicting the existence of black holes.
3. Being a leader is easy; you just stomp on the right heads when you need to.
4. The gopher chewed lustily on the discarded Fleshlight, but it failed to see the prowling cat.
5. Harris found his chewed-up Fleshlight on the golf course and recognized the gopher's foul work.

QUIZ 4: Count the clauses!
Look again at the sentences in Quiz 3, rewritten below. How many clauses are in each sentence?

1. When Albert Einstein was five, he saw his first naked woman.
2. When Einstein was five, he saw his babysitter having sex, and this led to his theories predicting the existence of black holes.
3. Being a leader is easy; you just stomp on the right heads when you need to.
4. The gopher chewed lustily on the discarded Fleshlight, but it failed to see the prowling cat.
5. Harris found his chewed-up Fleshlight on the golf course and recognized the gopher's foul work.

BONUS: analyze this awkwardly constructed sentence uttered by Tucker Carlson:

If you’ve got pronouns in your Twitter bio, you shouldn’t work here because we can’t trust you because you’re on the other side.

Of all the clauses you see in the above sentence (there are four clauses), which one is the independent (main) clause?

ANSWERS (highlight to make visible)

QUIZ 1
1. no
2. yes
3. yes
4. no
5. yes

QUIZ 2
1. dependent
2. independent
3. dependent
4. dependent

5. independent

QUIZ 3
1. complex
2. compound-complex (2 independent clauses: he saw + this led)
3. compound-complex (dependent clause: when you need to)
4. compound (2 independent clauses separated by comma-but)
5. simple (compound predicate: found... and recognized)

QUIZ 4
1. 2 clauses (When Einstein was..., he saw...)
2. 3 clauses (When Einstein was..., he saw..., this led...)
3. 3 clauses (Being is..., you stomp..., when you need...)
4. 2 clauses (gopher chewed..., it failed...)
5. 1 clause (simple sentence: 1 subject, compound predicate)

BONUS

The clauses beginning with "If" and "because" are all dependent clauses. The only independent clause, which is obviously the main clause, is you shouldn't work here.

I hope this helps. John.