Common mistakes

Some of the most common errors in student writing are sentence level errors, punctuation errors and word choice errors.

All sentences must be grammatically correct. Make sure you proofread your work thoroughly to check for the following sentence level errors.

Sentence fragments

A sentence fragment is an incomplete sentence.  Often, a sentence fragment is missing either a subject or verb.

✖Missing verb: The team of scientists the samples through the microscope.

✔With verb: The team of scientists examined the samples through the microscope.

✖Missing subject: When the report was delivered.

✔With subject: When the report was delivered, the committee debated the findings.

Fixing sentence fragments:

Make sure each sentence has both a subject and a verb.

Run-on sentences

A complete sentence with a subject and a verb is also called an independent clause. When two independent clauses are joined together incorrectly, this is called a run-on sentence. A run-on sentence has multiple subjects, each with its own verb.

✖Two independent clauses joined incorrectly: [independent clause 1] The Howard Coalition government, in 2001, wanted to prevent people seeking asylum arriving by boat [independent clause 2] this resulted in the government enacting what is known as the Pacific Solution.

Fixing run-on sentences:

The simplest way to fix run-on sentences is to add a full stop and capitalise the following word. The full stop should separate the first sentence from the second.

✔Two independent clasues joined correctly: The Howard Coalition government, in 2001, wanted to prevent people seeking asylum arriving by boat. This resulted in the government enacting what is known as the Pacific Solution.

You can also fix run-on sentences using coordinating conjunctions.

Subject-verb agreement

For a sentence to be grammatically correct, the subject and verb must “agree.” A common error is  when the subject is either singular or plural and the verb does not agree. The below examples look at present tense verbs.

With third person singular subjects (he/she/ t), in the present tense, add  “s” to the end of regular verbs.

✖Subject and verb don’t agree: A market rise because of investor optimism.

✔Subject and verb agree: A market rises because of investor optimism.

With third person plural subjects (they), in the present tense, do not add “s” to the end.

✖Subject and verb don’t agree: Doctors watches to see if any symptoms reoccur.

✔Subject and verb agree: Doctors watch to see if any symptoms reoccur.

Note that the “to be” verb is an example of an irregular verb. Irregular verbs do not obey the rules above.

With third person singular subjects in the present tense:

✔He/she/it: is

With third person plural subjects in the present tense:

✔They: are

For more information on subjects, verbs, irregular verbs, and subject-verb agreement see: English Grammar: The Basics.

Each sentence needs to be correctly punctuated. The most common punctuation errors are incorrect use of commas [link to grammar page comma section], comma splices and apostrophes [link].

Comma splices

A comma splice happens when two sentences or independent clauses are joined only with a comma and without a coordinating conjunction.

✖Comma splice: The Howard Coalition government, in 2001, wanted to prevent people seeking asylum arriving by boat, this resulted in the government enacting what is known as the Pacific Solution.

To fix a comma splice you can add a coordinating conjunction after the comma OR you can change the comma to a period.

✔Correct: The Howard Coalition government, in 2001, wanted to prevent people seeking asylum arriving by boat. This resulted in the government enacting what is known as the Pacific Solution.

Some errors involving individual words include the misuse of demonstrative pronouns and using an incorrect word.

Demonstrative pronouns

Demonstrative pronouns are words that either take the place of a noun or refer back to a noun.

Most frequently used pronouns: It, this, these, those, they, that

A common error is to start a sentence with a demonstrative pronoun without it being clear what this word refers back to.

✖Unclear use of “it”: Some of the empires most studied in the West include the Athenian empire, the Roman empire, and the British empire. It conquered most of the Mediterranean.

✔Correct: Some of the empires most studied in the West include the Athenian empire, the Roman empire, and the British empire. The Roman empire conquered most of the Mediterranean.

Another common error is for the demonstrative pronoun to not agree in number with its noun.

✖Demonstrative pronoun doesn’t agree with its noun: The building was condemned and slated for demolition. These were only built five years previously. [“These” refers back to “building” (singular) so the pronoun should be singular]

✔Correct: The building was condemned and slated for demolition. It was only built five years previously.

Common word errors

affect/effect

“Affect” is usually a verb and means to impact or change something.

✔Example: The vaccine affects the rate of transmission.

“Effect” is usually a noun indicating the result of change.

✔Example: The storm had a massive effect on the local population.

its/it’s

“Its” is a demonstrative pronoun indicating possession.

✔Example: The business was facing bankruptcy. Its gross mismanagement had ruined it financially. [“Its” refers back to “The business” and indicates that the “gross mismanagement” belongs to that business.]

“It’s” is a contraction of the words “it” and “is” or “has.”

✔Example: It’s hard to study in lockdown. [It is hard to study in lockdown.]

✔Example: It’s been a long time since I dined out. [It has been a long time since I dined out.]

would of/would have

“would of” is incorrect. Do not use.

“would have” is the correct form.

✔Example: The plague would have resurged in Europe were it not for the dedicated work of doctors.

Still have questions? Do you want to talk to an expert? Peer Learning Advisors or Academic Skills and Language Advisors are available.