Usually when sentence unity turns up on the agenda at the workshops I teach, participants look at me blankly. Who can blame them? The term, though a chapter heading in many grammar and writing texts, is vague at best. So I normally introduce the topic by explaining what sentence unity means.

Here are four possible explanations. Which one or ones are correctly worded?

1. Sentence unity is where you make sure the subject and predicate of a sentence join logically.
2. Sentence unity is when the parts of a sentence come together grammatically and make sense.
3. The reason sentence unity is important is because without it, a sentence is incoherent.
4. Sentence unity is taking care to keep sentence parts in line.

If you found fault with all of these sentences, congratulations. Their content is fine, but all four are awkwardly constructed. Each illustrates a sentence unity problem—a logical and grammatical hitch in how the subject and predicate join together. In each case the hitch centres on the verb to be.

To be, at first glance an innocent, workaday verb, can be surprisingly difficult to use correctly. Here’s a look at the most common ways writers misfire with this verb, destroying sentence unity in the process.

Is where

The word where, of course, denotes place. Yet writers often use where after the verb to be when referring to terms or concepts that have nothing to do with place. The result? Sentences like the following, which lack unity and suffer from both logical and grammatical problems.

• Origami is where you fold paper into shapes and objects that will delight and amaze the whole family.

The logical problem is that origami is not a place. It’s therefore not accurate to say that origami is where anything takes place. Here’s a possible revision:

• Origami is the art of folding paper into shapes and objects that will delight and amaze the whole family.

The grammatical problem is more complicated. If you’re a grammar keener, you’ll know that to be is a linking verb, and like all linking verbs it needs to be completed by either a noun or an adjective, or a phrase or clause that serves as a noun or an adjective. But where, a conjunction that refers to place, always begins an adverb clause.

Strictly speaking, this means that following to be with where should produce a grammatically disjointed sentence every time. Nowadays, however, only the most prescriptive grammarian would condemn the structure outright. It’s generally agreed that when the subject of the sentence is a place, it’s fine to use is where.

• China is where the art of paper-folding originated, but Japan is where it is most widely practised.

Is when

Is when wreaks the same sort of havoc in writing as is where. Consider this illogical sentence, which regrettably appears in an online writing guide from a California college:

• Unity is when all the sentences in a paragraph stick to the main point, as stated in the topic sentence.

The word when refers to time, but unity is not a time. This sentence is just as incorrect as the is where sentence above. It could be rewritten like this:

• Unity results when all the sentences in a paragraph stick to the main point, as stated in the topic sentence.

Like where, when is generally acceptable after the verb to be when its use is logical—that is, when its subject refers to a time.

• New Year’s Day is when many people resolve to kick nicotine forever.

The reason . . . is because

An even more widespread problem, the reason . . . is because is an expression that routinely springs to mind when we have some explaining to do.

• The reason Sheila left the fundraising dinner early was because she had had her fill of lame political jokes and leathery prime rib.

This sentence is snarled because because, like where and when, begins an adverb structure, not a noun or adjective structure, which should ideally follow to be. But unlike is where and is when, the reason . . . is because is uniformly panned by grammar texts and usage guides, largely because in addition to being grammatically suspicious, it’s redundant. The reason is and because mean the same thing.

It’s therefore best to avoid the reason . . . is because entirely. There are two easy fixes: (1) eliminate the reason . . . is and just keep because or (2) use that in place of because. The first approach is often better because it produces a more concise sentence.

• Sheila left the fundraising dinner early because she had had her fill of lame political jokes and leathery prime rib.
• The reason Sheila left the fundraising dinner early was that she had had her fill of lame political jokes and leathery prime rib.

To be in definitions

Anyone who has composed a definition knows the peculiar pain of trying to capture the essence of something in words. Part of the difficulty is that definitions so often hinge on the verb to be, which is almost an equals sign in such a sentence, equating the term to its definition. Definitions require a precise balancing of subject and predicate. Notice the awkwardness of these two attempts:

• A turophile is being a connoisseur or lover of cheese.
• Taxidermy is a lifelike representation of an animal constructed from its preserved skin.

Looking at the first sentence as if it were an equation helps to pinpoint the imbalance: a turophile (a person) = being something (an action). The sentence unity problem is clear: a person cannot equal an action. Here’s a better attempt:

• A turophile is a connoisseur or lover of cheese.

If we analyse the second sentence, we see that taxidermy (the process) = the representation of the animal (the stuffed animal itself). Once again, the sentence unity is askew. To be must be followed by a noun that says precisely what taxidermy is.

• Taxidermy is the craft of constructing a lifelike representation of an animal from its preserved skin.

Logic, balance and patience—that’s what it takes to construct unified sentences with to be. A simple verb that’s deceptively hard to use, to be is nonetheless a verb no writer can be without.

Test yourself