The Duolingo English Test (DET) has become a popular alternative to traditional English proficiency exams like the IELTS and TOEFL, especially for students seeking a convenient, affordable, and fast option. One of the key question types on the DET is "Error Detection," which evaluates your grammar accuracy and editing skills. To excel in this section, you must have a solid grasp of core grammar rules that frequently appear in academic and conversational English.
In this article, we will explore the top grammar rules you need to master to succeed in the Error Detection segment of the Duolingo English Test—along with examples and tips for improvement.
1. Subject-Verb Agreement
One of the most fundamental rules in English grammar is ensuring that the subject and verb in a sentence agree in number (singular or plural).
Rule: A singular subject takes a singular verb, and a plural subject takes a plural verb.
Examples:
✅ The dog runs fast.
❌ The dog run fast.
Tip: Watch out for sentences with inverted order or phrases between the subject and verb. These can confuse even advanced learners.
2. Tense Consistency
Maintaining consistent verb tense within a sentence or paragraph is crucial. Shifting tenses unnecessarily can create confusion and is a common error tested in the DET.
Rule: Use the same tense unless there’s a logical reason to shift.
Examples:
✅ She studied all night and completed her project.
❌ She studied all night and completes her project.
3. Incorrect Word Forms
This includes errors involving nouns, verbs, adjectives, and adverbs used in the wrong form. It is common in sentences where a student may confuse the grammatical role of a word.
Example Errors:
❌ He gave a quickly response.
✅ He gave a quick response.
Tip: Identify the role each word is playing in the sentence to determine the correct form.
4. Article Usage (a, an, the)
Articles are tricky for many learners, especially in cases involving abstract nouns or proper nouns.
Basic Rules:
Use “a” before words starting with consonant sounds.
Use “an” before words starting with vowel sounds.
Use “the” when referring to something specific.
Examples:
✅ I saw an elephant at the zoo.
✅ She is a doctor.
5. Pronoun Reference and Agreement
Make sure pronouns clearly refer to a noun and agree in number and gender.
Examples:
✅ Everyone should bring their own pen.
❌ Everyone should bring his own pen. (This can be outdated and non-inclusive.)
Tip: When in doubt, rephrase to avoid awkward or unclear references.
6. Parallel Structure
Parallelism means using the same grammatical structure for related words or phrases in a sentence. It improves clarity and flow and is a common focus in DET error detection.
Examples:
✅ She likes reading, writing, and jogging.
❌ She likes reading, to write, and jogging.
Tip: Check for consistency in lists, comparisons, or connected clauses.
7. Misplaced and Dangling Modifiers
Modifiers must be placed next to the word they are intended to describe. Misplaced modifiers can change the meaning of a sentence or make it confusing.
Examples:
❌ Walking through the forest, the birds were chirping loudly.
✅ Walking through the forest, she heard the birds chirping loudly.
8. Double Negatives
Using two negative words in the same clause creates confusion and is grammatically incorrect in standard English.
Examples:
❌ I don’t want no trouble.
✅ I don’t want any trouble.
Tip: Watch for combinations like “don’t…no,” “haven’t…nothing,” etc.
9. Preposition Usage
English prepositions often don’t follow the same logic as in other languages. The DET may test common collocation errors or idiomatic usage.
Examples:
✅ She is interested in music.
❌ She is interested on music.
10. Punctuation Rules
Improper punctuation can lead to grammatical errors, especially in complex or compound sentences.
Common Mistakes:
Comma Splice: Joining two independent clauses with a comma instead of a conjunction or semicolon.
Missing Commas in Introductory Clauses:
✅ After the meeting, we went home.
Final Tips for DET Grammar Preparation:
Read and edit English content daily to strengthen grammar awareness.
Break long sentences into parts and check each for grammatical accuracy.
Use AI-based tools or grammar checker extensions for real-time feedback.
Practice with Gurully’s Free DET Grammar Tests
To master the error detection section of the Duolingo English Test, regular practice is essential. Gurully offers free Duolingo English Test practice that includes grammar-focused exercises and mock tests modeled closely after the real exam.
By practicing regularly with Gurully’s DET resources, you can sharpen your grammar skills, boost your confidence, and improve your test score.
👉 Click here to start your Free DET Preactice
https://www.gurully.com/duolingo
Conclusion
Strong grammar is the foundation of excellent English proficiency, and the Duolingo Error Detection section puts your skills to the test. Reviewing these top grammar rules and practicing with realistic mock tests can make a significant difference in your DET performance. Start practicing today, and remember: consistency is key!
Let me know if you'd like the same blog converted into a short Instagram carousel or YouTube script.
