|The Structure of English Language - Conjunctions|
Conjunctions are joining words: they connect words, phrases, or entire clauses. There are two general kinds of conjunctive words: coordinate and subordinate.
Coordinate conjunctions join elements that are grammatically the same: two or more words, two equivalent phrases, or two equivalent clauses. The most common coordinate conjunctions are: and, but, or, for, nor, so, yet.
A correlative conjunction is a special kind of coordinate conjunction. It connects equivalent elements, but it works in pairs of words: both, and; either, or; neither, nor; whether, or; not only, but also.
Subordinate conjunctions. While coordinate conjunctions connect equal grammatical elements, subordinate conjunctions introduce dependent or conditional clauses.
Other word uses. Words that normally operate as conjunctions can often be used in other ways: as adverbs, prepositions, adjectives, or even pronouns.
There are other words besides conjunctions that serve as connectors (or connectives) in sentences. The relative pronouns who and which are often so used.
Some of the conjunctions work both as adverbs and conjunctions in the same sentence. This is often true of consequently, however, therefore, and nevertheless.
Note the semi-colon [ ; ]. This is standard here but is non-standard before but or and. (This appears to be changing, as speakers and writers treat words like nevertheless as conjunctions.)
It is possible to make clauses with conjunctions into separate sentences, especially when writing for literary effect.
In the second case the clause is so obviously dependent that it would not stand alone as a sentence and make sense. It can only be written that way for emphasis or some other effect.