In the English language, sentences are classified in two ways:
- by function--whether they state ideas, ask questions, give orders, or express surprise.
- by structure--by the number and types of clauses they contain.
Within this second classification, there are different types of structures:
- simple sentence--this type of sentence contains a single independent clause.
- compound sentence--this type of sentence contains two or more independent clauses joined by co-ordinating conjunctions such as and, but, or, not
- complex sentence--this type of sentence contains one independent clause and one or more subordinate clauses.
- compound-complex sentence--this type of sentence contains two or more independent clauses and one or more subordinate clauses.
A clause is a group of words with its own subject and verb acting as a predicate.
An independent clause can stand by itself as a complete sentence because it has a subject and a predicate that express a thought that needs no other phrase or clause for explanation.
e.g. Joe missed the sunrise. Joe=subject missed=verb [predicate]
A dependent clause contains a subject and verb, but it cannot stand by itself as a complete sentence; it can only be a part of a sentence.
e.g. Joe missed the sunrise because he awoke late.
The dependent clause because he awoke late needs clarification, so it is dependent. (the "why" part is missing)
Regarding the sentences to be qualified,
1. You can go by train or you can go by bus = a compound sentence because there are 2 independent clauses joined by the coordinating conjunction or.
2. My brother is an athlete = a simple sentence because there is only 1 subject and 1 verb [predicate] in a single independent clause.