Whether you have spoken English your entire life or are learning it as a second language, the difference between formal and informal speech is an important distinction to grasp. Identifying whether you are speaking to someone in a formal or informal way is indicative of the relationship between you and that person.
Informal speech uses contractions, whereas formal speech does not. Contractions are defined as a word that is shortened by leaving out some letters and replacing them with an apostrophe. An example is "can't," which is a contraction of "cannot."
In formal speech, a person should not end a sentence with a preposition, but in the case of informal speech, it is acceptable. Prepositions are defined as words or phrases that give the location of one noun or pronoun in relation to another noun or pronoun. An example of this is "The cat is under the table." In this sentence, the preposition "under" tells the reader the location of the cat in relation to the table.
Informal speech allows the deletion of relative pronouns. Formal speech, however, requires the pronouns. Relative pronouns are defined as words that attach a subordinate clause to the main clause. A subordinate clause is the part of the sentence that can't stand by itself, so the relative pronoun attaches it to the main clause. This creates a sentence that makes sense. In today's English language, there are only five relative pronouns: that, which, who, whom and whose. An example of a sentence using a relative pronoun: "I have never seen a movie that I did not like." In informal speech, one could say, "I have never seen a movie I did not like."
Determiners are words used with nouns, including articles such as a, an and the, possessive pronouns and indefinite pronouns such as this, that, these and those. In formal speech, determiners are usually used with the singular forms of verbs. In informal speech, determiners can be used with either a singular or plural verb. In formal language, you would say, "Neither of the answers is correct." In informal speech, you can say "Neither of the answers are correct."