All languages change over time. Consider all the new words that have been added to the English language in response to the developments in technology in recent years. Words like modem, gigabyte, or wi-fi were unknown until computers were invented. Words like mouse, tablet, or notebook carried very different meanings than what they might today.
Aside from changes in vocabulary, grammatical patterns change. As standard English is influenced by dialects from different parts of the United States or by foreign languages, new usages of words or phrases develop and may be incorporated into the standard language. The phrase "You are so hosed" is an indication of agreement with something said by another person - quite a change from speaking of a hose as a long tube used to squirt water.