Sentence structure

Sentences typically consist of one or more clauses, which can loosely be defined as a distinct part of a sentence that describes one action or event. Clauses come in two types: main (or independent) clauses and subordinate (or dependent) clauses. Sentences in an academic text need to contain at least a main clause. This means that you need a subject, or someone/something performing the action described by the verb, and a so-called finite verb, which is a verb that shows tense (past/present) and agreement in number with the subject (singular/plural). Here are two examples.

(1) The theory behind viral marketing [subject] is [finite verb: present, singular] relatively simple.

(2) Navigation systems [subject] are [finite verb: present, plural] essential in modern society.

In addition you may add subordinate clauses. Here are some of the most frequently used types of subordinate clauses.

Adverbial clauses starting with a subordinating conjunction: because, whereas, although:

(3) The option is lucrative for companies because it minimizes advertisement costs.
Subordinate clauses starting with that:

(4) The researchers found that half of the main characters of the most popular games are now female.
Relative clauses, starting with a relative pronoun:

(5) This server, which can host five hundred gamers, is one of the largest.
Non-finite clauses, starting with either an present participle (-ing) or with a past participle (-ed):

(6) This practice can also trigger intense discussions with online fan communities, giving rise to the cultural practice of theorizing.

(7) Founded in 2010, Instagram is one of the most successful start-ups in recent times.

Some important errors with sentence structure are the following.

Confusion between linking tools

Clauses can be joined using different linking tools: coordinating conjunctions, which connect two main clauses; subordinating conjunctions, which mark the beginning of a subclause; or linking adverbials, which don’t affect the grammar of the clause. These linking tools are different grammatically, but may be similar in meaning. Here are three versions of the same sentence, with each sentence containing a different grammatical linking tool which indicates contrast.

(8a) We expected a high number of cases, but this was not the case.

(8b) We expected a high number of cases, although this was not the case.

(8c) We expected a high number of cases. However, this was not the case.

Sometimes writers confuse words from different grammatical types, which can result in ungrammatical sentences. This happens most frequently with subordinating conjunctions when they are used as linking adverbials. Here are two examples.

(9) * Whereas, both articles support the idea that people activate perceptual symbols of reference during language comprehension.

(10) * Although, this sort of system is the right approach for people with disabilities.

The easiest solution is usually to combine this clause with the previous sentence or to replace the subordinating conjunction with a linking adverbial, as in the following rewritten versions.

(9a) Whereas both articles support the idea that people activate perceptual symbols of reference during language comprehension, they differ in their final conclusion.

(10a) However, this sort of system is the right approach for people with disabilities.

Of course, in order to get this right, you need to know the meaning and the grammar of linking words. Here is more information specifically about linking words.

Run-on sentences

You should always connect or separate clauses properly, to avoid so-called run-on sentences, as in the following examples.

(11) * Another way of generating energy is wind power it is renewable and better for the environment.

(12) * Different ways of walking affect the energy stored in the muscles therefore the way someone walks can make a large difference.

The most obvious solution to correct these sentences is adding punctuation to separate the two clauses properly and make two sentences.

(11a) Another way of generating energy is wind power. It is renewable and better for the environment.

(12a) Different ways of walking affect the energy stored in the muscles. Therefore, the way someone walks can make a large difference.

Other solutions are changing one of the clauses into a subclause or adding a different linking word which properly connects the clauses.

(11b) Another way of generating energy is wind power, which is renewable and better for the environment.

(12b) Because different ways of walking affect the energy stored in the muscles, the way someone walks can make a large difference.

Two other problems with sentence structure are so specific and common that we have a separate page on them.

Fragments

Fragments are incomplete sentences, which either lack a finite verb or only consist of a subordinate clause and no main clause. See the page on fragments for more information and solutions.

Comma splice errors

The term comma splice refers to a punctuation error that relates to sentence structure. The key to this error is the principle that a comma can’t be used between two main clauses, because the comma is not strong enough to properly separate or join two main clauses. Check the page on comma splices for the best solution.