Sentences are the unit of meaning in writing. Paragraphs, by contrast, are the unit of ideas. Individual sentences carry meaning, and several sentences together communicate ideas—sometimes sophisticated, complex ideas. It’s hard to communicate much with an individual sentence. The boy stood on the burning deck is certainly a meaningful sentence, but does not tell us much about why he was standing there, why the deck was burning, and what the circumstances were that led to the situation. We’d need more sentences in order to find out!
Academic writing should be written in complete sentences, unless you are asked to list ideas using dot points (e.g., acceptable when writing reports), or when engaged in a creative writing exercise (rare at university). All essay writing requires writing complete sentences. This begs the question: What is a complete sentence?
A complete sentence needs two parts:
- A subject: This is the part of a sentence containing a noun or noun phrase, e.g., The boy.
- In this case boy is the noun, and the is an article (or determiner). Together they make up a noun phrase
- A noun is a “naming” word; in a sentence the noun is often the subject of the sentence, i.e., what or who the sentence is about (although nouns can occur in other parts of a sentence too).
- The subject of a sentence is typically an object, a person or a group
- A predicate: This is the part of a sentence containing a verb that states something about what the subject is doing, e.g., stood. The predicate frequently includes the object of the sentence.
- In this case stood is the verb and burning deck is the object of the sentence. A object is part of a sentence that receives the action of the verb.
- A verb is a “doing” word.
- The verb describes what is happening in a sentence.
Together, the subject and predicate form what is called a clause. This is the smallest grammatical unit that results in a complete sentence. For example Jesus wept is a clause, and is therefore a complete sentence. It’s not a very interesting sentence though and you’d be hard-pressed writing an essay with sentences like that!
In English the structure of a sentence is subject + predicate (the former comprising the subject noun phrase; the latter comprising the verb + object), i.e., S-V-O, in that order. Other languages have a different order of these component parts, e.g., German orders its sentences in S-O-V form.
As we have seen, the object is not needed for a complete sentence, but it can improve the sentence by providing context, e.g.,
- Jesus wept on the cross
On the cross is a prepositional phrase consisting of a preposition, article and noun combination (on + the + cross). Cross is the object of the sentence in this case. An object in this example tells us where Jesus wept, or where the boy stood (on + the + burning deck).
Noun phrases can typically be longer than one or two words (The boy/Jesus), and in academic writing they are frequently very long indeed, e.g.,
- The American Nobel Laureate physicist Richard Feynman, in one of his more famous graduation addresses at Caltech, warned his audience of young science graduates about ‘cargo cult science’.
The trick is to look for the main verb in the predicate, in this case warned. To the left of this you should find the subject. The verb is the verb to warn, here expressed in past tense. Before it, there is a very long compound noun phrase:
- The American Nobel Laureate physicist Richard Feynman, in one of his more famous graduation addresses at Caltech
Breaking this down further: The subject comprises two noun phrases joined with a preposition in:
- The American Nobel Laureate physicist Richard Feynman
- One of his more famous graduation addresses at Caltech
together with a lengthy predicate:
- warned his audience of young science graduates about ‘cargo cult science’.
Put together in a tree diagram, we have the following component parts:
Fortunately, you don’t need to be able to do tree diagrams at university, but the example serves to show that, despite additional enhancements that can be made to sentences (adjectives, prepositions, pronouns, etc), the key information is subject + verb + object. The clause is the essence of a complete sentence.
Writing good sentences requires ensuring that every sentence has a subject and a predicate comprising at least a noun/noun phrase, a verb, and perhaps an object.
It’s important to know this as student often don’t write complete sentences. Instead they write sentence fragments (incomplete sentences). We look at fragments next.
Here’s an another example of a sentence:
- The explorer ran out of the building.
The subject is the explorer, and our verb is ran, because that’s what the explorer did. Because we have those two things, it works as a complete sentence. What would happen if we removed the second half?
- The explorer ran.
Is that still a complete sentence? Yes. It still contains our subject and predicate. We don’t need to say where they ran. It still makes sense and sounds fine. But what about the second half of the sentence?
- Out of the building.
Is that a complete sentence? Does it contain a subject or a verb? No. It contains a noun phrase the building, but that’s not the subject of the sentence, it’s the object. We don’t who or what is being discussed or how they came out! Both subject and verb are missing, so it’s not a complete sentence. This is called a sentence fragment.
Let’s now look at leaving the verb out of the sentence.
- The explorer.
The explorer … did what? We are left hanging. Adding the verb ran to it solves the problem. This is another example of sentence fragment.
So a complete sentence needs both a subject and a predicate. We don’t even need to understand the meaning of a sentence to know that subjects and predicates are needed for complete sentence formation. Chomsky made this clear in this famous example:
- Colourless green ideas sleep furiously.
This is a complete English sentence (albeit a nonsensical one):
- Colourless green: adjective (qualifies a noun)
- Ideas: Subject
- Sleep: verb
- Furiously: adverb (qualifies a verb).
Ideas sleep is also a complete sentence—even though it makes no sense! We look at sentence types next, and another way that sentence fragments can occur.
English sentences are of three main types: simple, compound and complex.
This contains one main clause* e.g.,
- The explosion destroyed every house on the block.
*A clause remember is the smallest grammatical unit that results in a complete sentence. This consists of a subject (noun phrase) and a predicate (containing a main verb).
This consists of two or more main clauses, usually connected by a coordinating conjunction (and, but, for, as, so), e.g.,
- Malaria is a problem in the region, but cholera is far more devastating.
In this example there are two clauses: Malaria is a problem in the region and Cholera is far more devastating. They are joined by the conjunction word but making a single thought with two parts. Compound sentences are desirable in academic writing as they make writing less “choppy” and they help to make for economy of ideas.
This consists of one independent clause and at least one dependent clause. One relies on the other. The main idea of the sentence is contained in the independent clause, creating an order of significance. This is by far the hardest type of sentence to write, however it gives English great subtlety.
- The students went to a party even though they had an assignment due.
- The actor, who had made many movies, died a lonely, broken man.
In these cases, the main ideas are (respectively): The students went to a party and The actor died a lonely, broken man. They are also the independent clauses because they stand-alone as sentences. The other clauses (dependent clauses) qualify the main clauses with further information.
These are hard sentences to write. For more on complex sentences see the helpsheet, Sentence Structure.
Sentence fragments are incomplete for two main reasons: 1) they lack a subject or a verb, or both (as we have seen); and 2) because they have an introductory (dependent) cause but not a main (independent) clause. Without the main clause, the thought is incomplete:
- Although the expedition involved a large crew.
- When the authorities finished reading the report.
- If the camera had been invented.
These sentences have subjects and verbs but the thought is incomplete because the main clause of the sentence is missing. We don’t know the issue the expedition faced, what the authorities did after reading the report, or what followed the camera being invented.
Students often write fragments like these: A dependent clause without its independent/main clause, i.e., an incomplete thought. This should be avoided.
Remember the rule: subject + predicate + complete thought.
Dependent and independent clauses are joined by words called subordinating conjunctions (because they subordinate one clause to another). Other examples:
- Cause/effect: because, since, so, that
- Comparison/contrast: although, even though, though, whereas, while
- Time: after, when, until, whenever, before
- Possibility: if, unless, whether, as if
- Place/manner: wherever, where how
Subordinators can also come in the middle of a sentence.
- The crew was famished after their long voyage.
- The explorer needed more ink even though he’d only written three pages.
The main, independent clauses here are:
- The crew was famished
- The explorer needed more ink.
The dependent clauses provide subordination and show a relationship between ideas.
Another way to connect complex sentences is by using relative pronouns (that, who, whose, which and whom), e.g.,
- The explorer, who had only written three pages, needed more ink.
Here the independent clause is: The explorer needed more ink, and the dependent clause is [The explorer] had only written three pages. The pronoun who joins the two clauses. NB: Note the punctuation used when interpolating relative clauses.
Subordinating conjunctions, as the name suggests, subordinate one clause to another more important clause (idea). Relative pronouns simply relate something to the main clause (without subordination). Compare the examples:
- The actor, who had made many movies, died a lonely, broken man. (relative pronoun)
- Although he had made many movies, the actor died a lonely, broken man (subordinating conjunction)
- After he had made many movies, the actor died a lonely, broken man. (subordinating conjunction).
Subordination, and the use of independent and dependent clauses, creates great subtlety. The first example above suggests it is incidental that the actor made movies. The second intimates that it is puzzling that the actor died lonely and broken because he should have made money and fame from his movies. The third makes it clear that his death occurred following a period of movie-making!
Be careful when using subordinating conjunctions and relative pronouns. You can easily say what you don’t mean!
Can you complete the sentences below by matching the independent and dependent clauses?
|1||After three years on the high seas,||a warrant was issued for the explorer’s immediate confinement.|
|2||Although the expedition crew all witnessed the discovery,||then the explorer would not have had to rely on inadequate writing skills.|
|3||When the authorities finished reading the report,||the explorer’s crew was exhausted.|
|4||If the camera had been invented,||not one other crew member could write as well as the explorer.|
Here are the answers to the previous exercise:
- After three years on the high seas, the explorer’s crew was exhausted.
- Although the expedition crew all witnessed the discovery, none of the other crew members could write about it.
- When the authorities finished reading the explorer’s report, they ordered him to be locked up.
- If the camera had been invented, then the explorer could have shown the jury his discovery and not relied on his poor writing skills.
Run-on sentences are another problem that occurs when writing. This is where two or more complete sentences, i.e., independent clauses, are joined together without making a clear connection or distinction between the ideas, i.e., they are joined together improperly.
An example is this:
- I love to write I would write a lot more if I had the time but I can’t my work just gets in the way.
It’s clear to see that these are really four complete sentences:
- I love to write.
- I would write a lot more if I had the time.
- I can’t [write].
- My work gets in the way.
These sentences can either be fixed by separating the sentences or joining them with a conjunction or two, and a subordinating connector, e.g.,
- I love to write and I would write a lot more if I had the time. But I can’t because my work just gets in the way.
Here’s another kind of run-on sentence called a comma splice (when two independent clauses are joined with a comma):
- Whales were often mistaken for sea monsters, in the past they damaged sailing ships.
The comma in the above sentence has ‘spliced’ the sentence. It would be clearer if you added a subordinating conjunction to show how the two ideas are related, like this:
- Whales were often mistaken for sea monsters because in the past they damaged sailing ships.
Here’s another example from a student’s assignment:
- Stem cells are able to replace any cell that dies any day, for instance cells that are present in our skill, blood and the lining of our intestines, and is the reason why we rely on stem cells, throughout our lives.
There are too many run-on ideas in this sentence, so it strains intelligibility. Commas are also in the wrong places. The meaning could be improved by putting one of the ideas into a sentence of its own, e.g.,
- Stem cells are able to replace any cell that dies any day; for instance, cells that are present in our skill, blood and the lining of our intestines. We rely on stem cells throughout our lives because of their capacity for cell replacement.
Remember: subject + verb + complete thought.
- If the thoughts are not connecting (are spliced by a comma), then add a subordinator or separate into a new sentence.
- If there are too many thoughts in the sentence, then separate it into at least two sentences.
When writing for assessment keep in mind the following:
- Short sentences (1-15 words) are easier to read than long sentences.
- Simple and compound sentences are easier to manage compared to complex sentences.
- There is nothing wrong with writing short sentences, particularly if the meaning is clearer. Don’t feel you must write long sentences just to ‘appear’ to be writing like an academic.
- The most important part of writing is to communicate your ideas. If you find that your longer sentences become confused, then remind yourself of the specific point you wanted to make and try not to put too many ideas into one sentence. Avoid complex sentences and write compound or simple sentences.
- Become familiar with writing in an academic style using simple sentences, and after that start exploring different sentence lengths and sentence types.
- Try not to use subordinating conjunctions at the start of a sentence, unless you intend to keep the sentence very short. The longer the sentence, the harder it is to control the meaning. Starting a sentence with although, while, though, because, etc., forces the writer to place the subject and main verb far from the beginning of the sentence. This is seldom done well. Take this example (actual student work):
- Because the economy of each country is becoming closer due to globalisation every country depends on the economy in other countries. (Compare: Globalisation means that every country depends on the economy of other countries.)
- Try not to use too many subordinating clauses: ‘Although he had made many movies, and while he was famous through the move-business, the actor died a lonely, broken man’. Too many subordinating clauses makes the sentence less clear. Stick to one subordinating clause per sentence, until you master clear writing.
- Keep the subject of the sentence and the main verb close to the beginning of the sentence. The reader needs to know what each sentence is about (subject), and what is being done (verb). See the example in the bullet point directly above. The subject is The actor, the verb is died: Although he had made many movies, the actor died a lonely, broken man’. Even better: The actor died a lonely, broken man, even though he made many movies. The subject and verb need to be close to the start of each sentence.
- Vary your subordinating conjunctions. If you need to use subordinating conjunctions, don’t overuse just one kind. Mix them up.
- Don’t let your sentences run-on!
Download our helpsheet on the topic, Sentence Structure.