There are many causes of semantic change:
1) Historical causes. According to historical principle, everything develops changes, social institutions change in the course of time, the words also change. Ex.: «car» which goes back to Latin «carfus» which meant a four wheeled (vehicle) wagon, despite of the lack of resemblance.
2) Psychological causes. Taboos of various kinds. Words are replaced by other words, sometimes people do not realize that they use euphemisms. Ex.: «lady;s room» instead of the «lavatory»
3) Linguistic causes. Tendency of a language to borrow a particular metaphorical development of a word from another language. Metaphor accounts for a very considerable proportions of semantic changes. Language is full of so-called fossilized (trite-банальный, избитый, неоригинальный) metaphors, which no longer call up the image of an object from which they were borrowed. Ex.: the leaf of a book; hands of a clock; a clock face; hands of a cabbage.