Grammar Rules You Should Know by Heart

Before Taking the ACT: Part II

Last week we discussed seven major grammar rules to learn and love before it comes time to take the ACT. Now that you’ve got those memorized – and I’m going to assume you do! – we can move on to seven more. (Don’t worry, these are the last seven, too.) Again, these grammar rules might sound confusing at first, but they’re pretty simple once explained a bit. If you can understand and memorize these before test day, you’re going to have a much better time taking the English portion.

All credit goes to Prep Scholar for this list!


“Use the correct idiomatic expression.”

OK, so…  this is one rule on this list that doesn’t really follow a formula, and there are no hard and fast rules. Some questions on the ACT will ask you to identify the phrase that works best in a sentence, and if it’s an idiomatic expression, you’ll simply need to rely on the answer that sounds best. I know, this advice is not that helpful. However, these can also be the easiest questions if you’re familiar with the idiom at hand! Let’s see some examples.

Incorrect: All students have the right for boycotting the pep rally.

Correct: All students have the right to boycott the pep rally.

Incorrect: I was late for curfew, and my mother was worried of me.

Correct: I was late for curfew, and my mother was worried about me.

These idiomatic phrases are sayings and common expressions used in everyday conversation. Hopefully, you won’t encounter any phrases you’ve simply never heard before!


“A pronoun must agree with its antecedent.”

This one is pretty straightforward. When selecting the proper pronoun to use in a sentence, choose the one that matches the noun it’s referring to! When in doubt, isolate the sentence and figure out exactly what the subject of it is.

Incorrect: My dad forgot to pick up their new shoes.

Correct: My dad forgot to pick up his new shoes.

Incorrect: My teammates and I were so excited to get their trophy.

Correct: My teammates and I were so excited to get our trophy.


“Use apostrophes correctly to form possessives.”

Memorize this: if a word is singular or plural and does not end in “s,” make it possessive by adding an apostrophe and an “s.” To make a plural word that ends in an “s” possessive, only add an apostrophe.

Incorrect: Andys new project is coming along very well.

Correct: Andy’s new project is coming along very well.

Incorrect: At the shelter, all of the dog’s kennels were dirty.

Correct: At the shelter, all of the dogs’ kennels were dirty.


“Colons must come after a complete sentence.”

You probably don’t use colons in your every day writing, so they can be a bit trickier. Just remember this: colons are used to introduce lists or explanations, and they can only be used after a complete sentenceIf you erased the explanation or list and swapped the colon with a period, the sentence should still make complete sentence. Let’s look at an example.

Incorrect: The things we needed to make the cookies included: eggs, butter, and sugar.

Correct: We needed several things to make the cookies: eggs, butter, and sugar.

If I deleted the listed items and removed the colon in the first example, I’m left with a fragment. The second one is correct, because the first part of the sentence could stand on its own.


“Semicolons separate two complete thoughts.”

If you deal with semicolons on the ACT, it’ll be identifying where a semicolon would work better than a comma or removing a semicolon that doesn’t work in the example. To get these questions right, memorize this: semicolons always separate two complete thoughts, a.k.a two phrases that could each stand alone as complete sentences! A comma can never do this – that’s called a comma splice, which we discussed in last week’s blog.

Incorrect: Because Caroline works so hard on these blogs; she genuinely hopes you read them.

Correct: Caroline works so hard on these blogs; she genuinely hopes you read them.

Incorrect: The storm was a massive one, all of the houses on the block flooded.

Correct: The storm was a massive one; all of the houses on the block flooded.


“Use the correct relative pronoun.”

Relative pronouns seem pretty simple in theory, but the ACT may try to test you on some tricky ones. The best thing you can do is to memorize the following list of what relative pronouns can refer to (although you likely already have most of them memorized, just by using English in your everyday life).

  • who and whom — people only
  • when — specific times or time periods only
  • where — places only
  • which — any noun other than a person
  • that — any noun
  • whose — possessive that can be used for people or things

Here are a couple of examples of incorrect and correct usage of relative pronouns, similar to what you might see on the ACT.

Incorrect: I prefer studying in libraries in which I can get free coffee.

Correct: I prefer studying in libraries where I can get free coffee.

Incorrect: We met a woman that had her purse stolen.

Correct: We met a woman who had her purse stolen.


“Subjects and verbs must agree.”

This is one of the very first things we learn in English class – but it’s easy to read a sentence quickly and mess this up! On the ACT, you may be asked to identify the proper verb to insert into a sentence, so make sure it matches the noun it’s actually referring to. It can be tricky if there are a few words in between the noun and the verb!

Incorrect: The shoes that I packed in my suitcase is heavier than I expected.

Correct: The shoes that I packed in my suitcase are heavier than I expected.

Incorrect: During the summer, many of my friends travels to different camps.

Correct: During the summer, many of my friends travel to different camps.


And there you have it! In total, there are 14 grammar rules you should have memorized by the time you sit down to take the ACT. However, many of these will likely come naturally for you – so focus on the ones that aren’t already second nature! With a little bit of practice and a few rules cemented in your brain, you’ll breeze through the English portion of the ACT.

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