How to classify a sentence

I was initially planning to write this week's post about different types of sentences, but then I needed to take a moment and figure out what that means. I had an idea of what I meant in my head, of course, but there are a number of different ways that one can conceptualise a sentence, and many reasons why it's useful to be able to distinguish its "type", using whichever system of categorisation is appropriate.

We may want to classify our sentences by how they're structured, in order to ensure we have variety and influence the flow and clarity of the larger piece. We may also want to categorise them by their purpose, especially if we've found ourselves in a bit of a tangle and need to figure out not just what the sentence is currently doing, but also what it needs to do. Therefore, what follows is a pair of the most commonly used forms of classification that you may find useful; think about what it is you're trying to figure out about the sentence, and choose accordingly.

Method 1: by grammatical function

This categorisation focuses on what the sentence is trying to achieve; are you making a statement, asking for something, giving an instruction? These four different types distil the sentence's function into the most basic expression of purpose: declaration, interrogation, imperative, and exclamation.

Declarative sentences

These are sentences where you are, when you really get down to it, just stating (or, if you like, "declaring") something:

These oranges don't look very ripe.

Usually, I wouldn't mind the rain, but today it was just one thing too many.

"Your Honour," Shelby began, "my client would like to ask for a short recess in light of this new evidence."

Declarative sentences make up the bulk of most pieces of writing, including descriptions, action, and a large part of communication and dialogue. They can be in first, second, or third person; they might be factual or subjective.

Interrogative sentences

"Interrogation" is another way of saying "question", so by that logic an "interrogative sentence" is just that: a question. (Do I need examples for this? Nah, y'all know what a question looks like.)

Imperative sentences

An imperative is a command or an instruction, therefore imperative sentences are those that direct someone to perform some sort of action:

Don't forget to pick up some milk on the way home from school.

Examine the patient's joints for range of movement.

Stuart Anthony Little, you get down from that tree right now!

Because these types of sentences are making a demand, they will always be in second person. You will find them most frequently in dialogue and in instructional writing.

Exclamatory sentences

Exclamations could be defined as "anything ending with an exclamation mark", but that leads to an awful lot of overlap with the other categories, so I'm going to define them as "an energetic statement that is expressive more than it is communicative", by which I mean things like:

Oh no!

Amazing!

Well, I never!

Gadzooks!

Great balls of fire!

They add a lot of flavour, and can express sudden upticks in emotion quite well, but don't communicate much information (like a declarative sentence) or directly engage with another party (like interrogative and imperative sentences).

Method 2: by level of complexity

These categories are less concerned with what is being said, and more with how it's being communicated. For this classification, we're looking at the structure of the sentence: is it simple and easy to follow; complex and interconnected; a compound of multiple "sub-sentences"? If you aren't already familiar with how clauses work, now would be a very good time to quickly read through my post on the different types of clauses before carrying on.

Simple sentences

A simple sentence is one that is made up solely of a single independent clause. This makes them the most straightforward structure of sentence, as they are centred on a single focus:

I very unfortunately had a migraine today.

There's a spick, span, and shiny police constable on every street corner for the parade.

Debbie couldn't find her pink shoes because her uncle's dog carried them off into the laundry when it visited the other day.

Using simple sentences may be preferable if you want to prioritise clarity in your writing, if you are portraying a simple or tightly focused mindset, or if you are speaking plainly about your topic. If (like me) you use a lot of compound and complex constructions in your writing, a short simple sentence can also provide some satisfying emphasis through contrast.

Compound sentences

Compound sentences are formed by attaching two independent clauses together, and are useful for showing the relationship between a pair of ideas:

The cats are particularly hyper tonight; maybe it's the weather?

Go to the store this afternoon, and I'll start making dinner while I wait for you to get back.

The safe was supposed to be secure, yet it had somehow been cracked open.

Compound sentences can deliver a lot more information with more nuance than simple constructions alone, but because we're working with the same fundamental building blocks we can still retain a lot of the benefits of clarity.

Complex sentences

The big difference between complex sentences and their simple and compound fellows is that they involve the use of at least one dependent clause alongside their single independent clause:

If the rain doesn't let up, we won't be able to go to the park.

Jude persisted in feeling anxious about the upcoming performance, despite their friends' efforts.

Deep under the mountain, the king of trolls sits upon his throne, which is built out of the bones of his enemies.

Dependent clauses add a further layer of nuance, and have a tendency to become tricky if they're being stacked. Each dependent clause is doing something slightly different to the independent clause at the heart of the sentence, and it can be easy to get a bit carried away with the modifications if you aren't paying attention.

Compound-complex sentences

As indicated by the name, a compound-complex sentence is one which combines the elements of compound and complex sentences to mix multiple independent clauses with any number of dependent clauses. This is where things get really interesting from a structural perspective:

There was a swing out front, and Billy was itching to play on it, but he'd have to go ask his mother first, if she was awake.

Because the Romans ruled so many far-flung corners of the known world, their rulers themselves came from a wide variety of places; very few of them were actually born in the great city itself.

First, we need to clear out the storage cupboard, since that hasn't been touched in years by this point, then we should move on to sorting out the boxes in the garage before it gets too hot, so that we still have time to tidy up the garden a bit as well—how does that sound to you?

By this point, we've lost much of the clarity of the simple sentence in the weeds of commas and conjunctions, and are potentially introducing a lot of related elements for the reader to keep track of. So if you are using a lot of compound-complex sentences, it's important to pay close attention to them and ensure that everything is lining up correctly and makes sense. The more clauses you have crammed together, the easier it is for meaning to get misrepresented or lost in the muddle.

Knowing how to classify sentences in different ways can be a useful tool for editing, as it makes it easier to know how you can fix a problem in the writing. If you can see that you're using a very long-winded compound sentence that needs to be punchier, you know that you have a structural problem that can be solved by splitting the sentence into a pair of simple sentences. If, however, your problem is that you have a declarative sentence that needs to be an imperative, that's a change in meaning that will require more context to adjust.

However you use these categories, understanding how your writing works is always the first step to improving your skills, and sentence function and structure are key elements to that; we have to use sentences whether we write fiction or non-fiction, and in every medium (except for some subsets of poetry, I suppose). Keep thinking about what you're doing, and happy writing!