Mathematics is easy. If you have two apples, and add two more, then you will have four.Originally Posted by queenbu
But language isn't like that. Language is a living thing; it evolves and changes over time, and it wasn't designed to be mathematical. Grammar is a way of looking at patterns that regularly crop up in a language and describing these patterns -- but there's no reason why there should be strict rules.
There are some languages with strict rules. Computer languages, for example. But some human languages have been invented with very regular and strict rules; one of them is Esperanto. In theory, it's a perfect language: the phonetics are very easy, the grammar rules are very simple and very regular. Yet few people speak it; for all that it is far easier to learn than English or French, it never became popular. Apart from anything else, it lacks a history, it lacks any culture, and it is a very sterile, boring language.
Real languages aren't invented by people sitting around saying, "Let's invent a language!" If you want to learn a language like that, you can learn Esperanto or even Klingon, but you won't be able to talk to many people. Real languages grow organically, and the people who speak them don't consciously follow rules. So we have lots of strange things, like the past tense of "to go" being "went" -- "went" comes from the old verb "to wend" which meant the same thing but is now only found in the phrase "to wend one's way". How did this happen? It just did -- for some reason we can only guess at, "to wend" fell into disuse, except for its past tense form.
Saying that grammars should always have strict rules is like saying that all trees should be exactly the same size and have perfectly straight branches. It simply doesn't happen that way.