There is a difference between the way we speak and the way we are taught to speak. Inherently, language is different for each person-- the environments in which we learn language in, the words that we hear, the way the words are strung together, and even the way words are pronounced gives each person an individual language, or an idiolect. And since this is the case, it can be difficult to understand why certain idiolects are often judged as not being as proper or intelligent as others.
Cultures attempt to regulate which languages and which language principles are used. This gap between what we "should" say and what we "do" say can be described using the linguistic terms prescriptive and descriptive grammar. Prescriptive grammar are the rules that we, as a community of language speakers, have set for ourselves to follow. In contrast, descriptive grammar is the way that we actually speak when communicating in a language.
To be more specific, while it is not grammatically correct to use "Me" instead of "I", many English speakers often say things like, "It was me who called you?" This is an example of descriptive grammar, since it is not grammatically correct, but it has been accepted and understood as "normal" by English speakers. Many linguists use the terms acceptable or unacceptable to describe descriptive grammar and proper or improper to describe prescriptive grammar.
So while it is improper to use "Me" instead of "I", it is acceptable in the general population of language speakers. However, if a language speaker violates the rules of descriptive grammar, the sentence is unintelligible and the meaning cannot be derived from it, making it both improper and unacceptable. For instance, if someone said "We were going to go right afterwards and like and be there and just like hopelessly wandering" the point of the sentence is not understood by the listener. This violates prescriptive and descriptive grammar rules.
Another example, "I'm going to the FFC, want to come with?" violates prescriptive grammar because it ends with a preposition. But ending with a preposition is a common way of speaking in the English language. Although the phrase is technically improper, it is an acceptable way of speaking when looking at descriptive language rules.
One of the reasons linguists use and support descriptive grammar instead of prescriptive grammar is because there is an inherent judgement about the value of a someone's sentence and idiolect when using prescriptive grammar. As long as the sentence structure and words can and are understood by the listeners of a language, the language should be seen as acceptable. The language of one class or culture is no better or more right than that of another class.
Dialects, or generalizations of similar idiolects by culture or region, vary due to environments, and the differences do not illustrate superiority. Saying that one dialect is worse than another would be equivalent to saying that English is better than Spanish, Japanese, or Korean. Neither language is more "right" than the other.
Today, there are many people who shame those who speak without prescribing to prescriptive grammar rules. One of these situations is Black English Vernacular (BEV) in which the dialect has a stigma-- and is looked down on by many who believe it is not "proper" or intelligent English. However, BEV has its own set of descriptive language rules that determine the acceptability. For instance, double negation is very common in BEV, saying, "I didn't do nothing" is common in BEV even though it might not be "proper" in the rules of prescriptive grammar that have been set in society.
As a result, stereotypes have resulted that affect the way other classes view BEV speakers. Black English Vernacular is just one example of hundreds of different dialects that can be found in English. There are pervasive prejudices toward non-standard dialects in our society. But because of what we know about descriptive and prescriptive grammar, these attitudes should no longer be valued or prevalent conceptions.
By eliminating the rumor that certain dialects are "better" than others, society will be able to accept different ways of speaking without placing values on certain ways of speaking. Prescriptive grammar is a way of looking at and analyzing language, but it shouldn't be the basis for which we judge the acceptability of language.
Descriptive language is the rule that linguists use because it eliminates the inherent stereotypes and value placements when comparing dialects and idiolects. The beauty of language is its infinite possibilities and arrangements, and descriptive language allows us to embrace these differences instead of judging them.