If it is based on a finite verb, it is called a finite clause. Since the team lost the match, the coach resigned. "Since the team lost the match" is a finite clause because the verb 'lost' is a finite verb.
If it is based on a non-finite verb, it is called a non-finite clause. The team having lost the match, the coach resigned. "The team having lost the match" is a non-finite clause because the verb 'having lost' is a non-finite verb (perfect participle).
What is important for us on this journey (i.e. to reach our destination - the answer to the question: 'what is a sentence?') is the route of finite clauses.
So in this article, we shall ignore the non-finite clauses.
Types of Finite Clauses
A finite clause may be independent or dependent.
Here are some famous examples of independent clauses:
"The light has gone out of our lives." (Jawaharlal Nehru)
"I have a dream." (Martin Luther King Jr.)
"The weak can never forgive." (Mahatma Gandhi)
These clauses are said to be independent because they are sufficient the way they are. They don't need any other group of words to depend upon. They can stand on their own.
Here are some examples of dependent clauses:
The light that shone in this country was no ordinary light.
You can learn grammar freely here, if you read these pages.
We are declaring to you what we have seen.
In the last three sentences above, we shall select the dependent clauses and see on what they depend.
'that shone in this country' depends on the independent clause 'the light was no ordinary light'.
'if you read these pages' depends on 'you can learn grammar freely here'.
'what we have seen' depends on 'we are declaring to you'.
Types of Dependent Clauses
They are of three types, depending upon the work they do.
See the three numbered sentences above.
Adjective (Relative) Clauses
In sentence 1—the clause 'that shone in this country' describes the noun light.
Words that describe a noun are called adjectives. Therefore, clauses that describe a noun are called adjective clauses.They are also known by the name relative clauses, because they always begin with a relative pronoun or relative adverb.
Adverb Clauses
In sentence 2—the clause 'if you read these pages' tells us something more about verb 'can learn'.
Words that tell us something more about verbs are called adverbs. Therefore, clauses which do the same job are called adverb clauses.
Noun Clauses
In sentence 3—We are declaring to you 'what we have seen'—if we ask the question, "are declaring what?", we get the answer 'what we have seen'.
A word which has this kind of relationship to a verb is called an object. To be an object is the privilege of nouns, pronouns, noun phrases, and noun clauses. So, 'what we have seen' is a noun clause.