#15104 Grammar Book 4: Prepositions and Conjunctions
A preposition is a small word such as 'in', 'on', 'after' etc. that describes a relationship between other words in a sentence. On their own, prepositions are difficult to define. However, when they combine with noun groups to make prepositional phrases, they help to qualify a noun or to tell when, where or under what conditions things happen.
Conjunctions are joining words. Conjunctions join words, phrases or clauses in a sentence. Conjunctions can also join two or more simple sentences.