2.2 Characteristics
Metaphor has conventional, systematic and abstract characteristics
(1) Conventional characteristic: Some metaphors are repeated used and have become common daily-used language. Most people have been unaware of their metaphorical meanings, such as arm of a chair, eye of a needle, face of a watch.
(2) Systematic characteristic: These metaphors reflect the characteristics of the systemic regulation of human cognition. Vehicle and body are combined so that we can see their own inner logic characteristic in metaphor.
(3) Abstract characteristic: When describing abstract things, metaphorical thinking helps people transfer these abstract concepts into a concrete form. Thus, it is possible for people to understand abstract ideas.

According to the analysis of metaphor, it can be seen that metaphor plays an important role in vocabulary learning.
To take water as an example, it can be corresponded with different target domains(Wang Wenbin, 2007: 143-150). such as :
above water (get rid of dilemma)、blow something out of the water(announce something)、draw water to one’s mill(only profits)、hold one’s water (do not say too much)、in deep water(in danger)、like water (generous)、back water (some place without vitality)、of the first water(with the best quality) and so on.

Similarly, sometimes, one target domain can correspond to different source domains such as marriage and love.
Marriage is somewhat like undertaking a project without instructions.
Marriage is like a lottery ticket that you cannot tear away though not winning the prize.
Marriage is a school for training men.
Marriage may often be a stormy lake, but celibacy is almost always a muddy horse pond.
Marriage is like wearing shoes; only feet know whether it is comfortable.
A happy marriage is a long conversation that always seems too short.

Love is a dream; but after one kiss one awakens to find it the truth.
Love is a chord in life , not a solo.
Love will travel through the time tunnel to shine like the sun and moon.
Love is the flame of life; without love everything will turn dark.
Love is like a mirror: once broken. that ends it.
Love is only the dirty trick played on us to achieve continuation of the species.

So it can be concluded that persity and flexibility of metaphor will beneficial to English learning . If only students know more about metaphor and form a metaphoric thinking style, it will be easier to learn vocabulary. 关于词汇的隐喻语际迁移的研究(2):http://www.youerw.com/yingyu/lunwen_10817.html