Sentence Structure: Building Blocks and Types

Every English sentence is built from the same kit: a subject, a verb, and patterns for adding the rest. Know the four sentence types and you can build — and repair — anything.

The Core Patterns

English sentences grow from five core patterns. Everything else is decoration on these frames.

• Subject + Verb: “Birds fly.”
• Subject + Verb + Object: “Birds eat seeds.”
• Subject + Verb + Complement: “Birds are beautiful.” / “She became a doctor.”
• Subject + Verb + Object + Object: “He gave her a book.”
• Subject + Verb + Object + Complement: “They named the baby Rose.”

The Four Sentence Types

Simple sentences carry one idea. Compound sentences join two ideas as equals with and/but/so (and a comma). Complex sentences rank ideas: a main clause plus a dependent clause (because, although, when, which). Compound-complex sentences do both — the workhorse of B2+ writing.

• Simple: “The library closes at nine.”
• Compound: “The library closes at nine, but the reading room stays open.”
• Complex: “Although the library closes at nine, members can return books anytime.”
• Compound-complex: “Because the budget shrank, the library cut its hours, and the students protested.”

Fragments and Run-ons: The Two Structural Errors

A fragment is a piece pretending to be a sentence — it lacks a subject, a verb, or a complete thought (“Because I was tired.” alone). A run-on crams two sentences into one without legal joints. Both are structure errors, not punctuation trivia: fix fragments by attaching them to their sentence; fix run-ons by splitting or by adding a comma + conjunction or a semicolon.

• Fragment: “Running through the rain.” → “We ran through the rain.”
• Fragment: “Because it was late.” → “We left because it was late.”
• Run-on: “It was late we went home.” → “It was late, so we went home.” / “It was late; we went home.”
• Test: a sentence must survive alone — subject, verb, complete thought.

Watch Out: Common Errors

Practice

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