English classifies sentences by how many clauses they contain and how they connect them. A simple sentence has one independent clause. A compound sentence joins two independent clauses, usually with a coordinating conjunction. A complex sentence combines an independent clause with one or more dependent clauses. A compound-complex sentence has at least two independent clauses and at least one dependent clause.

Type	Definition
Simple	One independent clause
Compound	Two independent clauses joined by a coordinator
Complex	One independent clause and one or more dependent clauses
Compound-complex	At least two independent clauses and one dependent clause

An independent clause can stand alone as a complete sentence. A dependent clause cannot stand alone because it depends on the main clause for complete meaning. In complex sentences, the independent clause is the core message, and the dependent clause adds information. Dependent clauses often begin with subordinators.

Clause Type	Definition
Independent	A clause that can stand alone as a sentence
Dependent	A clause that cannot stand alone and depends on a main clause

Subordination links a dependent clause to an independent clause using a subordinating conjunction. The subordinating conjunction shows the relationship, such as time, cause, condition, contrast, or purpose. The dependent clause can come before or after the independent clause, but punctuation rules may change. Subordination allows complex sentences to express detailed relationships between ideas.

Word/Phrase	Definition
because	It introduces a reason or cause
when	It introduces a time reference
if	It introduces a condition
although	It introduces contrast or concession
so that	It introduces purpose

In English, a dependent clause with a subordinator can come before or after the independent clause. When the dependent clause comes first, a comma usually separates it from the independent clause. When the independent clause comes first, no comma is usually needed before the dependent clause. This word order choice does not change the basic meaning but can change what is emphasized.

Rule
If a dependent clause comes before the independent clause, use a comma after the dependent clause
If the independent clause comes before the dependent clause, do not usually use a comma before the dependent clause

Coordination joins two independent clauses to create a compound sentence. In English, the most common coordinating conjunctions are for, and, nor, but, or, yet, and so. A comma usually comes before the coordinating conjunction when joining two independent clauses. Coordination links ideas as equal, while subordination makes one idea dependent on the other.

Word/Phrase	Definition
and	It connects ideas of equal importance or adds information
but	It connects ideas with contrast or an unexpected result
or	It connects alternatives or choices
so	It connects a cause and a result
yet	It connects contrast, similar to but, often with surprise

A relative clause is a type of dependent clause that describes a noun, usually introduced by who, which, or that. It adds information to a noun without starting a new sentence. In complex sentences, relative clauses help combine details efficiently. Punctuation depends on whether the information is essential or extra, but the clause remains dependent.

Word/Phrase	Definition
who	It introduces a clause describing a person
which	It introduces a clause describing a thing or idea
that	It introduces a clause identifying which person or thing is meant

Complex sentences use subordination to connect an independent clause with one or more dependent clauses, often with subordinating conjunctions or relative pronouns. Coordination joins independent clauses, typically with coordinating conjunctions, to form compound or compound-complex sentences. Mastering these patterns allows you to express detailed relationships and combine ideas clearly in English.