text: have you ever wondered why a roof wasn't named floor and a floor wasn't named a wall?   yes. vocubulary is arbitrary.  it's no different than using the word "monkey" in training your dog to sit.  sure, you could say "sit", but it's a dog, it associates the sound with the command.  now, because language has been in use with humans for between 50,000 and 250,000 years, we're quite a ways removed from the arbitrary naming of objects.  most all words today are a product of language evolution, so the simple answer to the roof/ floor question is : that's how the sounds evolved from earlier languages  the complex answer is that the earliest words were 'purportedly' onomatopaeic: meaning the word resembled the sound.  this is in modern examples like flush, swoosh, bark, boom, etc.  some linguists think that the earliest words in human vocabulary were us imitating the sound.....that perhaps we called a dog such because that was how we interpreted the sound.   a newer theory is one based on synesthesia, a phenomenon in which humans perception gets 'cross-wired'.  it's where we might 'see' music or 'hear ' color.  it's very rare, between 1 in 25,000 or 1 in 250,000 experiences it.  theoretically, all humans have it, only a small percentage retains it after the first 2-3 years of development.  this theory predicates that our first words were part of a synesthetic response to the action: the prime example being that you clench your teeth when you're angry or when you're punching or kicking you exert a sound....supposedly our 'action' words (also known as verbs) came from this response to forming our mouth in certain positions as we observed or experienced actions.