All English sentences can be classified as canonical and non-canonical clauses. Canonical clauses are the most basic sentences we can construct. They are also the most common. Here are examples of canonical and non-canonical clauses:
Canonical: Oliver has finished his report.
Non-Canonical: Oliver hasn't finished his report.
Canonical: Alexandra is coming for lunch.
Non-Canonical: Is Alexandra coming for lunch?
Canonical: The workers knew the truth.
Non-Canonical: He said that the workers knew the truth.
Canonical: She missed her last bus.
Non-Canonical: Either she missed her last bus or it was late.
Canonical: The maid stole the vase.
Non-Canonical: The vase was stolen by the maid.
From the examples, we see that canonical clauses are affirmative. Negatives clauses are non-canonical.
Canonical clauses are declarative. Interrogatives are non-canonical. This is also true of imperatives (Please come now!) and exclamatives (What a beautiful day!).
Main clauses are canonical. If we add a subordinate clause (that the workers knew the truth), we have a non-canonical clause.
Canonical clauses are simple sentences. If we have a compound sentence with a correlative conjunction such as either or, we have a non-canonical clause.
Canonical clauses are in active voice. If we use passive voice, we have a non-canonical clause.
Canonical clauses are the most elementary of English syntax. They are in active voice and are main clauses, simple clauses, affirmatives and declaratives. Other types of clauses are classified as non-canonical.