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Give me a for instance...
If you mean changing of e.g. ortography, pronounciation, grammar(Irregular verbs esp.): It is because there are disagreements between linguists...
And language can also change with adding new words and/or expressions. Usu. by slang, young pupulation speech, etc...
Btw. if you wanted to write plural of the noun REASON, you should know that apostrophe is used to form possessives of nouns, to show the omission of letters AND to indicate certain plurals of lowercase letters. To make plural of a noun, you add -s, -es(if nouns ends in S, or has voiceless sound on the end, or the ending letter contains in its structure voice S, etc.), or you have irregular plural(e.g. mouse-mice), etc. ;)
Language change 
Re: Language change 
Linear Mode
