Every sentence you write — whether it’s a tweet, an email, or a novel — starts with the same foundation: a subject and a predicate. Without these two parts, your words can’t form a complete thought.
In this guide, we’ll break down what a sentence really is, explain subjects and predicates in simple terms, and show you how to spot (and fix!) common sentence mistakes.
1️⃣ What Is a Sentence?
A sentence is a group of words that expresses a complete thought. To be a sentence, it must have two parts:
➡ a subject (who or what the sentence is about)
➡ a predicate (what the subject does or is)
Together, they form a statement that makes sense on its own.
✅ Examples of complete sentences:
➡ First person (active):
I finished the report this morning.
➡ First person (passive):
The report was finished by me this morning.
➡ Second person (active):
You wrote an excellent introduction.
➡ Second person (passive):
The introduction was written by you.
➡ Third person (active):
She delivered the packages on time.
➡ Third person (passive):
The packages were delivered by her on time.
➡ Simple present active:
They play soccer after school.
➡ Simple past passive:
The game was won by the home team.
👉 All of these are complete sentences — they have a subject and a predicate, and they express a full thought.
🚫 Examples of sentence fragments:
➡ Wrote an excellent introduction.
(Missing subject — who wrote it?)
➡ After the meeting.
(Missing the subject and the predicate. This is a clause.)
➡ The packages on the table.
(Missing predicate — what about the packages?)
➡ Because she was late.
(Dependent clause — doesn’t stand alone as a complete thought.)
➡ Running through the park.
(Missing subject and/or verb that completes the idea.)
💡 Tip: When checking if something is a complete sentence, ask:
- Who or what is this about? (subject)
- What is it doing or being? (predicate)
- Does it make sense on its own?
2️⃣ What Is the Subject?
The subject is the part of the sentence that tells us who or what the sentence is about. It’s the person, place, thing, or idea that performs the action or is described by the predicate.
📌 Simple subject:
The main word or words that name the subject without extra detail.
📌 Complete subject:
The simple subject plus any words that describe or modify it.
✅ Examples:
➡ Simple subject:
The dog barked.
👉 Dog is the simple subject.
➡ Complete subject:
The loud, black dog barked.
👉 The loud, black dog is the complete subject.
➡ Simple subject:
She runs every morning.
👉 She is the subject.
➡ Complete subject:
My best friend from college runs every morning.
👉 My best friend from college is the complete subject.
➡ Simple subject:
Books fill the shelves.
👉 Books is the subject.
➡ Complete subject:
Old, dusty books from the attic fill the shelves.
👉 Old, dusty books from the attic is the complete subject.
💡 Tip:
To find the subject, ask:
👉 Who or what is doing the action?
👉 Who or what is the sentence about?
3️⃣ What Is the Predicate?
The predicate tells what the subject does or is. It contains the verb and all the words that describe the action or provide information about the subject.
📌 Simple predicate:
The main verb or verb phrase (the action or state of being).
📌 Complete predicate:
The verb + all the words that tell what the subject does or is.
📌 Compound predicate:
When the subject does more than one thing — two or more verbs or verb phrases joined by a conjunction (like and, or, but).
✅ Examples:
➡ Simple predicate:
The dog barked.
👉 Barked is the simple predicate.
➡ Complete predicate:
The dog barked loudly at the mail carrier.
👉 Barked loudly at the mail carrier is the complete predicate.
➡ Compound predicate:
The dog barked and chased the mail carrier.
👉 Barked and chased the mail carrier is the compound predicate — two actions linked by and.
➡ Simple predicate:
She writes.
➡ Complete predicate:
She writes every morning before breakfast.
➡ Compound predicate:
She writes every morning and edits her work in the evening.
💡 Tip:
When the same subject does multiple actions, that’s a compound predicate.
4️⃣ Putting It Together: Complete Sentences
Now that you understand subjects and predicates, here’s the key to writing complete sentences:
👉 A sentence must have both a subject and a predicate, and together they must express a complete thought.
If either the subject or predicate is missing, or if the words don’t form a complete idea, you have a fragment, not a sentence.
✅ Examples of complete sentences:
➡ Simple structure:
The rain stopped.
(Subject: The rain / Predicate: stopped)
➡ More detail:
The loud, sudden rain stopped as quickly as it began.
(Subject: The loud, sudden rain / Predicate: stopped as quickly as it began)
➡ Compound predicate:
The rain stopped and the sun came out.
(Subject: The rain / Predicate: stopped and the sun came out → Note: this has two subjects in one sentence — actually a compound sentence)
➡ Another example with compound predicate:
She packed her bag and left for the station.
(Subject: She / Compound predicate: packed her bag and left for the station)
🚫 Examples of fragments:
➡ Stopped as quickly as it began.
(Missing subject)
➡ The loud, sudden rain.
(Missing predicate)
➡ After the sun came out.
(Missing complete thought — dependent clause)
💡 Quick test:
Ask yourself:
👉 Who or what is this about? (subject)
👉 What happens or is said about them? (predicate)
👉 Does it stand alone as a full idea?
5️⃣ Common Sentence Structure Errors
Even experienced writers sometimes slip up when it comes to complete sentences. Here are the most common sentence structure mistakes — and how to avoid them.
🚫 1️⃣ Sentence Fragments
A fragment is a group of words that looks like a sentence but is missing a subject, a predicate, or doesn’t express a complete thought.
✅ Examples of fragments:
- After the meeting. (missing predicate)
- Ran through the park. (missing subject)
- Because she was late. (dependent clause — incomplete thought)
✅ How to fix:
Add the missing part so it forms a full idea:
- After the meeting, we went for coffee.
- She ran through the park.
- Because she was late, we started without her.
🚫 2️⃣ Run-on Sentences
A run-on happens when two complete sentences are joined incorrectly (without punctuation or the right conjunction).
✅ Example of run-on:
She finished her work she went home.
✅ How to fix:
- She finished her work. She went home.
- She finished her work, and she went home.
- After she finished her work, she went home.
🚫 3️⃣ Comma Splices
A comma splice is when two independent clauses (complete sentences) are joined with only a comma.
✅ Example of comma splice:
I love writing, it helps me relax.
✅ How to fix:
- I love writing. It helps me relax.
- I love writing because it helps me relax.
- I love writing, and it helps me relax.
💡 Tip:
When in doubt, read the sentence aloud. If you hear a natural stop or a new idea, check that you’ve punctuated or connected it correctly.
Understanding what makes a sentence complete — the subject and the predicate — is the foundation of clear and effective writing. By recognizing these parts and avoiding common errors like fragments and run-ons, you can improve your grammar, make your writing easier to read, and communicate your ideas more confidently.
Keep practicing by breaking down sentences you read or write into their subjects and predicates. With time, this skill will become second nature — and your writing will be stronger for it.