Prescriptive vs Descriptive grammar
As we look at the use of language, we should specifically stick to descriptive grammar because prescriptive grammar based on a set of rules about how people especially those who think they own a language- or so called native speakers-think language should be used. In a prescriptive grammar there is right and wrong language,where the right use of language depends on the standards set by a group of individuals who feel offended when others speak a language without following the proper grammar. A good example is when a Kenyan may use a sentence like-Ng'ombe itakayoingia zizini itakamwa ( or kamuliwa) maziwa. For the users of Kiswahili, the message has already been conveyed although the sentence is grammatically wrong. The correct sentence would be Ngombe atakayeingia zizini atakamwa maziwa.

  If we say that the first sentence is wrong, because the noun ng'ombe should be in A-Wa (Ngeli)class( M-WA for the analog generation like me) we are becoming prescriptive Kiswahili grammarians and this is prejudice. For speakers whose L1( First language) is Luo or Luhya or Gikuyu, it is normal to call any animal with the neuter personal pronoun it which translates to i kiwakilishi cha nafsi  katika ngeli ya i-zi (for the analog generation we used to call this class Ngeli ya N ). We become prescriptive if we demand that the people who use a particular language as their L2( second language) should use it the way we want them to use it and according to the standards that  we have set.

However, on the other hand we should be gracious to users of a second language by encouraging communicative language use. Here is where a descriptive grammar, which is a set of rules based on how language is actually used comes in. The American rejected prescriptive grammar by writing their own Dictionary and developing their own English.