In grammar, a conjunction is a part of speech that connects two words, phrases or clauses together. This definition may overlap with that of other parts of speech, so what constitutes a "conjunction" should be defined for each language. In general, a conjunction is an invariable grammatical particle, and it may or may not stand between the items it conjoins.
The definition can also be extended to idiomatic phrases that behave as a unit with the same function as a single-word conjunction (as well as, provided that, etc.).
Types of conjunctions
Coordinating conjunctions, also called coordinators, are conjunctions that join two or more items of equal syntactic importance. Coordinating conjunctions include for, and, nor, but, or, yet, and so. The mnemonic acronym FANBOYS may be used to remember these, with each letter being the initial letter of a conjunction. It is often stated that these seven words are the only coordinating conjunctions; however (at least in British English) others have been identified including whilst, now, and nor, and but nor
Correlative conjunctions are pairs of conjunctions that work together to coordinate two items. English examples include both … and, (n)either … (n)or, and not (only) … but (also)....
Subordinating conjunctions, also called subordinators, are conjunctions that introduce a dependent clause. The most common subordinating conjunctions in the English language include after, although, as much as, as long as, as soon as, because, before, if, in order that, lest, since, so that, than, that, though, unless, until, when, whenever, where, wherever, whether, while. Complementizers can be considered to be special subordinating conjunctions that introduce complement clauses (e.g., "I wonder whether he'll be late. I hope that he'll be on time"). Some subordinating conjunctions (although, before, until, while), when used to introduce a phrase instead of a full clause, become prepositions with identical meanings.
In many verb-final languages, subordinate clauses must precede the main clause on which they depend. The equivalents to the subordinating conjunctions of non-verb-final languages such as English are either clause-final conjunctions (e.g. in Japanese), or suffixes attached to the verb and not separate words
Such languages in fact often lack conjunctions as a part of speech because:
1.the form of the verb used is formally nominalised and cannot occur in an independent clause
2.the clause-final conjunction or suffix attached to the verb is actually formally a marker of case and is also used on nouns to indicate certain functions. In this sense, the subordinate clauses of these languages have much in common with postpositional phrases.
Coordinating conjunctions
For: indicates reason (used as a synonym of 'because'), or purpose
And: used to connect words, phrases, or clauses
Nor: presents an alternate negative idea
But: indicates a contrast or exception
Or: presents opinions, alternates, or substitutes for ideas of equal importance
Yet: connects ideas that follow logically and are contrary
So: shows the consequences of related ideas
