1)Simile(明喻)：It is a figure of speech which makes a comparison between two unlike elements having at least one quality or characteristic in common. To make the comparison,words like as, as……as, as if and like are used to transfer the quality we associate with one to the other. For example, As cold waters to a thirsty soul,so is good news from a far country.
2)Metaphor(暗喻)：It is like a simile, also makes a comparison between two unlike elements, but unlike a simile, this comparison is implied rather than stated.For example, the world is a stage.
3)Analogy(类比)：It is also a form of comparison, but unlike simile or metaphor which usually uses comparison on one point of resemblance, analogy draws a parallel between two unlike things that have several common qualities or points of resemblance.