SECTION 1
Why Finding Errors Matters
People have cared about using words correctly for thousands of years. In ancient Greece and Rome, teachers called grammarians (experts in language rules) taught students how to speak and write clearly. They believed that using the right words showed that you could think clearly too.
Over time, people created dictionaries and grammar books to record the "correct" way to use words. Today, standardized tests like the TACHS (Test for Admission into Catholic High Schools) check whether you can spot errors in writing. This skill helps you become a better writer and reader.
~400 BCE • Ancient Grammar Studies
1755 • Johnson's Dictionary
1800s • Grammar in Schools
1900s–Today • Standardized Testing
So how do you actually find an error hiding in a sentence? That is the question we will answer in this lesson. You will learn the most common types of mistakes and a step-by-step method for catching them.
SECTION 2
Core Principles of Error Identification
On the TACHS, you will see a short passage broken into numbered lines. Your job is to find the line that contains a mistake in word usage (choosing the wrong word) or sentence usage (building a sentence incorrectly). Sometimes there is no error at all. Let's look at the main ideas behind this skill.
Word Choice Errors
Subject-Verb Agreement
Verb Tense Errors
Pronoun Errors
No Error Option
KEY TAKEAWAY
SECTION 3
Visualizing the Error-Finding Process
The diagram below shows the step-by-step process you should follow when you see an error-identification question on the TACHS. Start at the top and move down through each check. This flowchart will help you build a habit of reading carefully.
Notice that the flowchart has four checkpoints. You do not need to memorize fancy grammar terms. Just ask yourself four simple questions at each line: Is the right word used? Do the subject and verb match? Are the verb tenses consistent? Do the pronouns match what they refer to? That is all it takes.
SECTION 4
How Common Errors Work
Commonly Confused Words
Many TACHS questions test commonly confused words. These are pairs or groups of words that sound similar but have different meanings. Here are some of the most important ones to know.
| Word | Meaning | Example |
|---|---|---|
| their | belonging to them | Their dog is friendly. |
| there | a place, or used to introduce | There is the library. |
| they're | they are | They're going to the park. |
| your | belonging to you | Your backpack is open. |
| you're | you are | You're doing great. |
| accept | to receive or agree to | I accept the award. |
| except | not including | Everyone except Maria left. |
| affect | to influence (verb) | Rain will affect the game. |
| effect | a result (noun) | The effect was amazing. |
Commonly Confused Word Pairs
Subject-Verb Agreement Rules
A singular subject takes a singular verb, and a plural subject takes a plural verb. A tricky part is when extra words come between the subject and verb. For example: "The box of chocolates is on the table." The subject is "box" (singular), not "chocolates." So "is" is correct.
Verb Tense Consistency
When a passage is written in the past tense, all verbs should stay in the past tense unless there is a good reason to switch. For instance, "She walked to the store and buys some apples" incorrectly shifts from past ("walked") to present ("buys"). It should say "bought."
SECTION 5
Classifying the Most Common Error Types
The diagram below organizes the error types you are most likely to see on the TACHS. Think of it as a quick-reference guide. Each branch shows a different category of mistakes along with an example.
Test-Day Tip
SECTION 6
Worked Example: Finding the Error
Let's walk through a sample TACHS-style question together. Read the passage below, which is split into four lines.
Sample Passage
Step-by-Step Error Search
- 1
Step 1 — Read the Full Passage
Read all four lines from start to finish to get the overall meaning. The passage is about a science fair. It uses the past tense throughout ("were displayed," "explained," "asked," "announced"). So far, the tense seems consistent. - 2
Step 2 — Check Word Choice in Each Line
Line 1: "displayed in the gymnasium" — all words are correct. Line 2: "explained there experiment" — wait! "There" means a place. The sentence needs "their," which means "belonging to them." This is a word choice error.Error found on Line 2: "there" should be "their." - 3
Step 3 — Confirm by Checking the Other Lines
Line 3: "The judges asked thoughtful questions" — subject "judges" (plural) matches "asked" (plural). Good. Line 4: "the principal announced the winners" — correct word usage and agreement. No errors in Lines 3 or 4. - 4
Step 4 — Select Your Answer
Because Line 2 contains the word choice error ("there" instead of "their"), you would select Line 2 as your answer.Answer: Line 2
SECTION 7
Strengths and Pitfalls of Different Strategies
There are different ways students try to find errors on the TACHS. Some strategies work better than others. The table below compares three common approaches so you can pick the one that works best for you.
| Strategy | Strengths | Pitfalls |
|---|---|---|
| Read aloud in your head | Helps you "hear" errors that look normal on paper. Good for catching awkward phrasing. | Can be slow. Some errors (like their/there) sound the same, so you might miss them. |
| Line-by-line checklist | Systematic and thorough. You check every category of error for every line. Least likely to miss something. | Takes more time. Requires you to remember the checklist. Needs practice to become fast. |
| Jump to the line that "feels wrong" | Very fast. Experienced readers often spot errors by instinct. | Risky if you are guessing based on feelings. May skip the real error or choose a correct line. |
Comparing Error-Finding Strategies
KEY TAKEAWAY
SECTION 8
Connecting to Advanced Writing Skills
The error-identification skill you are learning now is not just for the TACHS. It is a stepping stone to more advanced writing and editing skills. In high school and college, you will move from spotting errors to revising (improving sentences for clarity) and editing (polishing grammar, spelling, and style). The table below shows how the skills build on each other.
| Skill Level | What You Do | Example |
|---|---|---|
| Identify Errors (Now) | Find the line with a mistake in word or sentence usage. | Spot "there" when it should be "their." |
| Correct Errors (Next) | Not only find the mistake but choose the correct replacement. | Replace "there" with "their" in the sentence. |
| Revise & Edit (Advanced) | Improve sentences for clarity, flow, and style — even if there is no "error." | Rewrite a correct but clunky sentence to make it clearer and more engaging. |
How Error Identification Leads to Advanced Skills
By getting really good at spotting errors now, you are building a strong foundation. Every great writer is first a great editor. The more errors you can catch, the stronger your own writing will become.
SECTION 9
Practice Problems
Try these five practice problems. For each one, read the lines and decide which line contains an error in word or sentence usage. If no line has an error, choose "No error."
Question 1: CONCEPTUAL
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Question 2: BASIC
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Question 3: INTERMEDIATE
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Question 4: APPLIED
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Question 5: CRITICAL THINKING
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SUMMARY
Lesson Summary
Summary
To identify the line with an error on the TACHS, check for four main types of mistakes: word choice errors (like confusing "their," "there," and "they're"), subject-verb agreement errors (making sure the subject and verb match in number), verb tense inconsistencies (keeping past, present, or future tense consistent), and pronoun agreement errors (making sure pronouns match the nouns they replace).
Use a line-by-line checklist approach: read the full passage first, then go through each line checking for word choice, agreement, tense, and pronouns. If every line is correct, choose "No error". Remember, finding the true subject of a sentence — ignoring extra words between the subject and verb — is one of the most important tricks for getting these questions right.