A very long time ago, I wrote a post claiming that "who vs. whom" was not actually tested on the ACT (despite the fact that "who" and "whom" do both appear as answer choices) and was soundly told off by a number of readers for posting something so blatantly inaccurate.
So I'm going to admit I was wrong...partially. Yes, "whom" is sometimes the right answer. And yes, the ACT does often test a version of the "who vs. whom" rule, but only at a relatively superficial level. If you have a reasonable knowledge of what standard English sounds like, you can probably hear the errors involving those words. You don't necessarily need to know anything about grammar, although of course that can't hurt.
Many people are familiar with the story of how the Pilgrim settlers met a Pawtuxet tribe member named Squanto whom befriended them, taught them how to survive in their new wilderness home, showed them how to plant crops, and acted as an interpreter with the Wampanoag tribe and its chief, Massasoit.
A. NO CHANGE
B. which befriended them
C. who befriended them
D. and befriending them
Yes, "who vs. whom" is clearly being tested here, but there's a pretty good chance that you can hear that "whom befriended" just sounds really awkward and that "who befriended" sounds a lot better -- even if you don't know anything about grammar.
The simplest version of the rule here is that "whom" should never be used right before a verb. That's it. In order to apply the rule, you do need to be able to accurately recognize verbs, but if you can do that, you're pretty much set.
Now here's part two of what you're likely to see -- it involves "whom," but it does *not* involve "who."
Many people are familiar with the story of how the Pilgrim settlers met Squanto, a Pawtuxet tribe member from whom they learned about planting crops and surviving in the New World.
A. NO CHANGE
B. from who
C. by which
D. from which
The rule here is that "whom," not "who," must follow a preposition when you're referring to a person, and "from" is a preposition. C and D out because "which" should only refer to a thing. So A is correct.
Generally speaking, though, ACT is a lot more interested in having people know the basics of correct English and not make flagrant mistakes than in knowing every little nitpicky grammar rule. That means you're exceedingly unlikely to see a question that looks like this:
Many people are familiar with the story of how the Pilgrim settlers met Squanto, a Pawtuxet tribe member who they encountered shortly after arriving in the New World.
A. NO CHANGE
B. whom they encountered
C. which they encountered
D. they encountered him
To answer this question, you have to know the rule for real and recognize that the correct word is the direct object of the verb "encounter" (they encountered *him*, not *he*). "Whom" is therefore correct because it is an object pronoun, whereas "who" is a subject pronoun. But again, the chance of your encountering a question that tests the rule at this level of subtlety is very, very small.
Dashes are one of the punctuation marks pretty much guaranteed to show up on ACT English. They are tested in three ways, the first extremely common, the other two comparatively rare.
1) To set off a non-essential clause (2 Dashes = 2 Commas)
In this case, dashes are used exactly like commas to indicate non-essential information that can be removed without affecting the basic meaning of a sentence. If you have one dash, you need the other dash. It cannot be omitted or replaced by a comma or by any other punctuation mark. This is the most important rule regarding dashes that you need to know for the ACT.
Correct: John Locke - whose writings strongly influenced the Declaration of Independence - was one of the most important thinkers of the eighteenth century.
Incorrect: John Locke - whose writings strongly influenced the Declaration of Independence, was one of the most important thinkers of the eighteenth century.
2) To introduce an explanation or a list (Dash = Colon)
In this case, a full, stand-alone sentence must come before the dash, the way it does before a colon. The information that comes after the dash does not have to be a full sentence, although it's perfectly fine if it is.
When a dash is used in the same way as a colon, you will never be asked to choose between them -- only one option will be given.
Correct: A number of John Locke's ideas influenced the Declaration of Independence - particularly those concerning government, labor, and revolution.
Correct: John Locke was one of the most important thinkers of the eighteenth century - his writings strongly influenced the Declaration of Independence.
So if dashes have the same function as colons (and as semicolons when they separate two full sentences), why bother to use them at all? Why not just use a colon or a semicolon instead?
3) To create a dramatic pause
The answer is that dashes can be used to create a break in a thought - they force the reader to stop for a fraction of a second before continuing on to whatever idea comes next. They can therefore be used to create a sense of drama or suspense, even a very slight one.
Complete ACT Punctuation Rules
Commas should be used:
1. Before a Coordinating Conjunction to join two full sentences (Independent Clauses)
Coordinating Conjunctions, aka FANBOYS:
For, And, Nor, But, Or, Yet, So
And and But are the two most popular conjunctions on the ACT; other coordinating conjunctions appear only rarely.
Correct: London is a very old city, but some parts of it are extremely modern.
2. Between a dependent clause and an independent clause when the dependent clause comes first.
Dependent clauses are clauses that cannot stand on their own as full sentences. They begin with Subordinating Conjunctions such as before, after, because, when, and since.
Dependent Clauses (the underlined words make the clauses dependent -- without them, the clauses would be independent):
-Because I went home
-After we returned from the movie
-When we visited Chicago
In the following sentence, the dependent clause is in bold and the independent clause is underlined
Correct: Because London is a very old city, it has buildings from many different eras.
When “strong” subordinating conjunctions such as (Al)though and Even Though are used to start a dependent clause, a comma should be used between the dependent clause and the independent clause, regardless of which one comes first.
Correct: London is a very old city, although some parts of it are extremely modern.
Correct: Although London is a very old city, some parts of it are extremely modern.
3. To indicate non-essential words or phrases A non-essential clause is simply a clause that can be removed from a sentence without affecting its essential meaning. It's like a little interruption.
Non-essential clauses are always surrounded by commas.
Correct: London, which is a very old city, has some extremely modern parts.
Incorrect: London which is a very old city, has some extremely modern parts.
Incorrect: London, which is a very old city has some extremely modern parts.
The same goes for single words:
Correct: London is a very old city. It does, however, have some very modern parts.
Incorrect: London is a very old city. It does however, have some very modern parts.
Incorrect: London is a very old city. It does however, have some very modern parts.
4. Around names and titles when used restrictively
With comma: Last night I went to see a movie with my friend, Joe.
Without comma: Last night I went to see a movie with my friend Joe.
The first sentence means that you have one friend and that his name is Joe. The second sentence means that you have more than one friend, one of whom is named Joe. When you place a comma before a name or a title, you are indicating that there is only one of those people or books (movies, etc.); when you do not use a comma, you are indicating that the person, book, movie, etc. you are referring to is simply one among others.
5. After introductory words and phrases
Correct: In the beginning, there was light.
Correct: Finally, the teacher handed back the papers.
Correct: Meanwhile, Rob and I waited in the car.
6. To separate items in a list
Comma before and is optional
Correct: Hiking, skiing, and white-water rafting are my favorite things to do.
Correct: Hiking, skiing and white-water rafting are my favorite things to do.
7. To separate adjectives whose order could be reversed
Correct: The groaning, rumbling train finally pulled into the station
Correct: The rumbling, groaning train finally pulled into the station
Commas should NOT be used:
1. Between two full sentences (Independent Clauses)
When two stand-alone sentences are joined by a comma, the result is known as a Comma Splice, which is always incorrect.
Incorrect: London is a very old city, some parts of it are extremely modern.
2. Between an independent clause and a dependent clause when the independent clause comes first.
In the following sentence, the independent clause is underlined and the dependent clause is in bold.
Incorrect: London has buildings from many different eras because it is a very old city.
3. Between two clauses with the same subject when the subject is not repeated
Repeated Subject: London is a very old city, but it has many modern buildings.
Subject Not Repeated - Correct: London is a very old city but has many modern buildings.
Subject Not Repeated - Incorrect: London is a very old city, but has many modern buildings.
4. Between Subjects and Verbs
Correct: Carlos and his sister are going to a concert tonight.
Incorrect: Carlos and his sister, are going to a concert tonight.
5. In Compound Subjects and Compound Objects
Correct: Carlos and his sister enjoy attending movies and concerts.
Incorrect Compound Subject: Carlos, and his sister enjoy attending movies and concerts.
Incorrect Compound Object: Carlos and his sister enjoy attending movies, and concerts.
6. Before or after prepositions
Correct: My birthday is my favorite day of the year.
Incorrect: My birthday is my favorite day, of the year.
Incorrect: My birthday is my favorite day of, the year.
7. Before or after the word That
Correct: I finally saw the movie that my friends had recommended.
Incorrect: I finally saw the movie, that my friends had recommended.
Incorrect: I finally saw the movie that, my friends had recommended.
AND in clauses in which that is optional and does not appear:
Correct: He said he would come to the movie tonight. (=He said that he would come to the movie tonight)
Incorrect: He said, he would come to the movie tonight.
8. Between two adjectives whose order cannot be reversed
Correct: I was somewhat taken aback by the sight of the big blue dog.
Incorrect: I was somewhat taken aback by the sight of the big, blue dog.
(You wouldn't say, "I was somewhat taken aback by the sight of the blue, big dog").
9. Between adjectives and nouns
Correct: The sight of the big blue dog surprised me.
Incorrect: The sight of the big blue, dog surprised me.
10. Before an open parenthesis
Correct: The Caribbean Sea contains some of the world's most stunning coral reefs (which are home to thousands of species of marine life), but many of them are in danger because of overfishing and pollution.
Incorrect: The Caribbean Sea contains some of the world's most stunning coral reefs, (which are home to thousands of species of marine life), but many of them are in danger because of overfishing and pollution.
Semicolon = Period
Semicolons are used:
1. Between independent clauses without a conjunction
London is an old city; it has many new buildings.
2. Before However and Therefore when they are used to begin a clause
London is an old city; however, it has many new buildings.
London is an old city; therefore, it has buildings from many different eras.
Colons are used:
1. Before a list
I like the following sports: hiking, swimming, and rafting.
2. Before an explanation
Ex: I talked to my teacher yesterday, and here's what she said: I should stop by tomorrow before class to discuss the test.
Colons must always follow a full sentence that can stand on its own as a complete thought. Unlike semicolons, however, they don't have to be followed by one.
Correct: These are the kinds of fruit I like: apples, bananas and strawberries.
Incorrect: I like: apples, bananas and strawberries.
Dashes are used:
1. To indicate non-essential statements within a sentence
Grammatically, they are identical to two commas when used this way.
Correct: London - which is a very old city - has many new buildings. (= London, which is a very old city, had many new buildings)
2. Before a list, an explanation, or to create a deliberate pause in a sentence
Grammatically, they are identical to colons when used this way
Correct: I like the following kinds of fruits - apples, bananas and strawberries. (= I like the following kinds of fruits: apples, bananas, and strawberries.)
Apostrophes are used to make nouns possessive
For singular nouns, always add apostrophe + -s
The boy's ball = The ball belonging to the boy
The albatross's blanket = The blanket belonging to the albatross
For plural nouns, always add -s + apostrophe (or -es + apostrophe if the singular version ends in -s)
The boys' ball = The ball belonging to the boys
The albatrosses' blanket = The blanket belonging to the albatross
It's vs. Its
It's = It is
Its = Possessive form of it Its' = Does not exist
Correct: It's raining outside now, but it should be sunny tomorrow.
Incorrect: Its raining outside now, but it should be sunny tomorrow.
Correct: The book is missing its cover.
Incorrect: The book is missing it's (not: it is) cover.
You're vs. Your
You're = You are
Your = Possessive form of you
Correct: I'm sure whether you're (you are) coming with us tonight.
Incorrect: I'm sure whether your coming with us tonight.
Correct: This is your jacket, right?
Incorrect: This is you're (not: you are) jacket, right?
They're vs. Their vs. There
They're = They are
Their = Possessive form of they
There = A Place
Correct: Bob and Alice are our friends, and they're (they are) coming to dinner tonight.
Incorrect: Bob and Alice are our friends, and their/there coming to dinner tonight.
Correct: The books are missing their covers.
Incorrect: The books are missing they're/there covers.
Correct: We went to my favorite restaurant last night, and I think I left my jacket there.
Incorrect: We went to my favorite restaurant last night, and I think I left my jacket they're/their.
Who's vs. Whose
Who's = Who is
Correct: I don't know who's (who is) at the door.
Incorrect: I don't know whose at the door.
Whose = Possessive of who
Correct: I don't know whose jacket this is.
Incorrect: I don't know who's jacket this is.
That's vs. Thats
That's = That is
Thats = Does not exist
Correct: That's (That is) my jacket lying over there.
Incorrect: Thats my jacket lying over there.
Hers vs. Her's
Hers = Possessive form of her
Her's = Does not exist
Correct: This jackets is hers.
Incorrect: This jacket is her's.
I find that a lot of people are afraid of semicolons. Either that, or they sort of kind of think they might have an idea about how to use them... From what I have observed, semicolons are probably the most misunderstood punctuation mark. Which is very unfortunate because they're actually very simple to use. They also show up on the SAT (Fixing Sentences only) and ACT English a whole lot.
Here's the rule:
Semicolon = Period
That's it (well, almost). Seriously. Wherever you can use a period, you can also use a semicolon. If you want to get a tiny bit more technical about it, a semicolon is used to join two independent clauses, but you don't even need to go that far.
There's one more tiny little piece, though: whenever you start a clause with "however" or "therefore," you need to place a semicolon before it, thereby attaching it to the previous sentence. It is 100% incorrect to use a comma, and technically you shouldn't use a period either.
Correct: It's very sunny outside now; however, it might rain later.
Incorrect: It's very sunny outside now, however, I heard it might rain later.
Incorrect: It's very sunny outside now. However, I heard it might rain later.
Prepositions are Location and Time words.
They tell us where things are and when they happen(ed).
Common Prepositions: To, From, For, At, Beside, With, Without, Of, Between, In, Out, On, On top of, Under, Over, Above, Below, Beneath, Through, Before, After
A prepositional phrase is a phrase that starts with a preposition (shocking, I know!). For the purposes of the SAT and ACT, prepositional phrases consist primarily of prepositions, nouns/pronouns, and adjectives. They do not contain verbs.
-At my house
-During the movie
-Between you and me
-To my older sister
If you're not sure whether a word is a preposition, see if you can place it right before a noun at the end of a sentence. For example, you can say, "My friend and I went to the movie" because to is a preposition, but you cannot cannot say, "My friend and I went when the movie" because when is not a preposition.
In addition, one of the most frequent questions students ask me is how they can figure out where prepositional phrases begin and end. The answer: a prepositional phrase begins at the preposition and ends right before the verb (if there is one).
In the following sentences, the prepositional phrases are underlined. Note that a sentence can easily contain multiple prepositional phrases back to back, and that a prepositional phrase can occur anywhere in a sentence.
-The stack of books is sitting on the kitchen table.
-One of the stories on the front page of the newspaper discusses the upcoming elections in great detail.
-The train is crowded with people on their way home from school and work.
-Sitting on the table are a peach and an apple.
Prepositional phrases are frequently inserted between subjects and verbs on both the SAT and the ACT in order distract from disagreements, so whenever you don't immediately see an error in a sentence, it's a good idea to cross out all the prepositional phrases.
Most of my students are astounded to learn that as a high school freshman I was required to memorize Strunk and White's legendary grammar guide, The Elements of Style. After all, that was the sort of thing students had to do in 1965, not 1995.
I was, however, lucky enough to have a teacher who had been teaching since 1965, and frankly, memorizing the "little book,"as William Strunk referred to it, was one of the most useful things I ever did. The Elements of Style covers most of the grammar found on the SAT Writing section, and it's an invaluable tool for learning to write clearly and rigorously. I had no idea that the book would help me so much in the standardized testing process; no one ever mentioned it, and at that point, I was far more concerned with surviving ninth-grade English (which was, hands down, the most difficult class I ever took).
But that brings me to a point that is all too easily forgotten: sometimes the best way to prep for a test is not to spend all your time prepping for a test, and some of the best test-prep material is not found in test-prep books. If you're a junior and you have two weeks -- or two days -- to cram for the SAT, that's a different story, but if you're just starting to the process, try to approach it a little differently. Having the capacity to express yourself in a clear, logical, and persuasive manner is important in and of itself, not just because it's something that's tested on the SAT.
Thanks, Mr. V.
And if you want to buy The Elements of Style:
Dangling modifiers are guaranteed to show up on both the SAT and ACT. On the former, they're by far the most common error tested on Fixing Sentences (there are usually at least two per section, sometimes three, very occasionally four); on the latter, they usually only appears once or twice per test, but they also have a habit of showing up when you least expect and are therefore easy to overlook.
So what is a dangling modifier, and how do you fix it? Dangling modifiers are best explained through examples, so let's take a look at an example.
Correct: The dog jumped over the fence after escaping from its leash.
In this sentence, the subject (the dog) appears immediately and the modification follows. We can, however, also rewrite the sentence so that the modification comes before the subject:
After escaping from its leash, the dog jumped over the fence.
Even though the dog no longer appears at the beginning of the sentence, it is still the subject. And at the beginning of the sentence, we now have a clause that describes the subject but that does not name it. If the subject does not immediately follow that description, however, the result is a dangling modifier. When taken literally, sentences that contain dangling modifiers are often completely absurd.
Dangling Modifier: After escaping from its leash, the fence was jumped over by the dog. (Implies that the fence escaped from its leash.)
Dangling Modifier: After escaping from its leash, jumping over the fence was what the dog did. (Implies that jumping escaped from its leash.)
While some of the dangling modifiers that appear on the SAT and ACT clearly sound wrong, like the sentences above, others can be much harder to catch -- especially if you're not looking out for them. For example:
Dangling Modifier: Having focused on celebrity gossip for most of its existence, it came as a surprise to many readers that the magazine began printing stories devoted to more serious topics.
Dangling Modifier: Having focused on celebrity gossip for most of its existence, many readers were surprised when the magazine began printing stories devoted to more serious topics.
Since dangling modifiers often start with gerunds, the appearance of the phrase "Having focused" at the beginning of the sentence is a tip-off that we are dealing with a dangling modifier. The question we must then ask is: What focused on celebrity gossip for the majority of its existence?
So the magazine must come immediately the comma. It does not matter that the meaning of the sentence is clear in the other versions; they are grammatically incorrect regardless. When dealing with dangling modifier questions, you must first identify the subject.
Correct: Having focused on celebrity gossip for most of its existence, the magazine began printing stories devoted to more serious topics and thus surprised its readers.
We can also rewrite the sentence entirely so that the subject appears at the beginning:
Correct: Because the magazine had focused on celebrity gossip for most of its existence, its readers were surprised when it began printing stories devoted to more serious topics.
On the SAT, answer choices for dangling modifier questions usually follow a highly predictable pattern. Three answers will not fix the dangling modification and can be eliminated automatically. Of the two answers that remain, one will be awkward and/or create a fragment (usually the longer one), and the other one will be correct. Less often, the sentence will simply be rewritten completely.
On the ACT, there will be only one answer that correct eliminates the dangling modifier.
This is a shortcut that can save you a huge amount of time on the ACT. If more than one of these constructions appear as answer choices, you can automatically eliminate them.
Why? The ACT will never provide more than one correct answer. If two answers say exactly the same thing, then neither can be chosen over than the other, and both must therefore be wrong.
Let me give you an example. Consider the following sentence:
Since they were first domesticated nearly 40,000 years ago, dogs have played an important role in many human societies.
(A) No change
(B) ago dogs
(C) ago. Dogs
(D) ago; dogs
Because a period and a semicolon are the same thing, neither one can be correct, and we can actually eliminate options C and D without even looking at the sentence.
That immediately leaves us with just A and B to check out (the answer, in case you're wondering, is A). No plugging in, no puzzling over whether that semicolon really looks right, just two answers gone.
This post was inspired by Robin Koerner's little rant in the Huffington Post about his encounter with a job applicant who had a 3.9 GPA but no idea of how to use an apostrophe correctly.
While you can, in real life, break some of the rules the ACT tests without anyone really noticing, you cannot break this one. Sure, your high school or even your college teachers may overlook it, but if you screw this up on your resume or even in an email to a potential employer or college interviewer, it may very well be noticed and count very seriously against you. In many cases, it can lead to a flat-out rejection. Employers actually don't care about your critical-thinking skills unless you can express yourself in basic, coherent English. If you don't believe me, check out this article from the Washington Post.
Of all the basic rules to mess up, apostrophe usage will stick out the most, so if you learn even one thing while studying for ACT English, please let it be this. Besides, apostrophes are always tested on the ACT; mastering them can get you an easy couple of points.
I've already discussed the rule for it's vs. its in another post and have covered apostrophe usage for other pronouns (you're, that's, we're, they're) on my complete guide to ACT punctuation page, so here I'm just going to stick to nouns.
An "-s" by itself is used to make a noun plural. No apostrophe is needed.
Correct: I have two dogs at home.
Incorrect: I have two dog's at home.
An apostrophe is needed, however, to make a noun possessive -- that is, to indicate that it belongs to someone or something.
Correct: This is my dog's toy. (= This is the toy that belongs to my dog.)
Incorrect: This is my dogs toy.
An apostrophe is also needed when forming a contraction between a noun and the verb "is."
Correct: My dog's not feeling well today. (= My dog is not feeling well today).
Incorrect: My dogs not feeling well today.
The place where most people get tripped up is when dealing with nouns that are both plural and possessive. In these cases, the apostrophe is placed after the "-s."
Correct: These are my dogs' toys. (= These are the toys that belong to my dogs.)
Incorrect: These are my dogs toys.
Incorrect: These are my dog's toys. (= These are the toys that belong to my dog, not my dogs. This version is grammatically correct but changes the meaning of the sentence.)
When you encounter these types of questions on the ACT and are not immediately sure of the answer, you need to break them down into steps.
First you need to determine whether you are talking about something possessive. That will determine whether you need an apostrophe at all.
Next determine whether the noun in question is singular or plural. If it's singular, the apostrophe comes before the "-s;" if it's plural, the apostrophe comes after.
Let's consider the following (real) ACT sentence:
The sound of the distant honking of these majestic birds always makes me look up.
F. NO CHANGE
The first thing we need to figure out is whether "birds" should in fact be plural, and word "these" indicates that it should (you wouldn't say "These majestic bird"). So we definitely need an "s-" on the end of "birds."
The only question is whether there needs to be an apostrophe.
This is where this question gets a little tricky. The phrase "honking of the birds" does indicate possession, but it takes the place of the apostrophe. We can say either "the majestic honking of the birds" OR "the birds' majestic honking" but not "the majestic honking of the birds'". So no apostrophe, which leaves us with F and G (the answer is F).
If you're still on the fence about whether you should take the SAT or the ACT, or if you've been prepping for one test all along and are thinking of taking the other one, here's a very general overview of what you should know about the grammar for each exam:
The SAT places a very heavy emphasis on the following:
-Verb tense (particularly various forms of the past tense)
-Modification (dangling and misplaced)
And tests the following frequently as well:
-Idiomatic phrasing (prepositions and gerunds vs. infinitives)
-Adjective and adverb usage
-Logical relationships between clauses (conjunctions)
-Relative pronouns (who, which, in which, etc.)
Diction and Redundancy problems are tested rarely.
Punctuation is covered only minimally: the only two punctuation marks tested are the comma and the semicolon. The former is only tested in regard to using coordinating (FANBOYS) conjunctions to join independent clauses, and to creating non-essential clauses within a sentence. The latter is tested only in regard to joining independent clauses and before certain conjunctive adverbs (however, therefore, moreover, consequently), never to break up excessively length sentences.
Dashes, apostrophes, and colons are not explicitly covered.
For the most part, the SAT tests various grammar rules in isolated sentences. Only in the Fixing Paragraphs section (6 questions) does context come into play. While this does make SAT Writing simpler in some regards, the sentences are also more complex and contain more constructions that high school students are likely to be unfamiliar with (and thus likely to erroneously believe are incorrect). The "No error" option, particularly in the Error-Identification section, means that many test-takers find this section of the SAT to be very tricky.
The biggest difference between the SAT and and the ACT is the format. All ACT questions are presented in the context of a passage, forcing students to pay close attention to context and to employ both reading and writing skills simultaneously. An answer that is grammatically correct may thus not be the right answer if it is inconsistent with the style or or tense of the surrounding sentences, or does not logically fit in with the information presented in the paragraph or passage in which it appears. In comparison to SAT sentence, which often deal with literary or historical themes, ACT passages tend to focus on more quotidian matters.
Strictly in terms of grammar, however, the ACT is a more punctuation-oriented test than is the SAT. Commas are not only tested extensively in relation to independent and non-essential clauses but also in relation to dependent clauses and adjectives.
Test-takers are also required to identify the incorrect use of commas in many more ways than on the SAT: between compound subjects and objects, between multiple adjectives, before prepositional phrases, between subjects and verbs, and before relative clauses with and without "that" (usually the most difficult for test-takers to identify).
Other punctuation marks tested include the following:
-Semicolons (to separate independent clauses and before the conjunctive adverb "however")
-Colons (before lists and explanations)
-Dashes (to set off non-essential information and explanations)
-Apostrophes (its vs. it's, etc.)
Common non-punctuation concepts tested include:
-Subject-verb agreement (only a couple of questions per test at the most, usually in the form of subject-prepositional phrase-verb)
-Verb tense and form (often context-dependent)
-Adjective vs. adverb
-Dangling and misplaced modifiers (only a couple of questions per test)
-Clarity and conciseness
-Diction and register (too casual vs. appropriate for a formal piece of writing)
In short, there is actually a substantial area of overlap between the two tests. Each has its own quirks (some people who are used to taking the SAT find the constant back-and-forth of the ACT disconcerting at first), but the majority of the material covered is similar. Deciding which test to focus on is ultimately a matter of figuring out which one feels more comfortable.