Over time, as needs change, the contract changes and what I need to say to transfer information changes. More importantly, I have to keep track of several contracts because not all listeners have signed the same one! This is called code-switching, and it's why I talk to my boss differently than to my much younger niece than to my mechanic.
Language prescriptivists don't seem to understand that and will refer to their favorite dictionary and grammar guide (usually published sometime between the 18th and 19th centuries and written by people of the same ilk trying desperately to coax order from chaos) as if they contained the great laws handed down from the God of Languages and will try and convert the World by force to sign the contract that they think all the world should be on.
There are no rules in language, only guidelines.