The use of metaphor in poetry is one of the most important aspects of poetic style that must be mastered. Metaphor can be described as figure of speech in which a thing is referred to as being something that it resembles. For example, a fierce person can be referred to as a tiger. Another example of a metaphor would be the description of a person who was uncommunicative as being as "silent as stone". The word stone is an image that is used to explain the intense silence of the person. In this way, metaphors are used in poetry to explain and elucidate emotions, feelings, relationships other elements that could not to described in ordinary language. Poets also use metaphor as a way of explaining or referring to something in a brief but effective way.
An easy way to understand metaphor is to view a metaphor as a simile without the word "like". A simile compares two things in a clear fashion. For example: "he is like a beast". Another example of a simile would be to say that the man is so fierce that he is like a tiger. A metaphor assumes that the relationship will be understood without the interlinking word "like".
Metaphor works on many levels in poetry. The best way to show how a metaphor function is to study the use of sustained metaphor. Sustained metaphor refers to a metaphor that consistently runs through the entire poem and is therefore easily identifiable. Metaphors that are sustained also provide a depth and inner complexity to the poem