先看一道OG题

　　With sea otters tokeep the population of sea urchins in check, kelp forests can flourish. InfACT, even two years or less of sea otter presence can reduce the sea urchinthreat in a coastal area. Without sea otters present, nevertheless, kelpforests run the danger of becoming barren stretches of coastal wasteland knownas urchin barrens.

　　A.NO CHANGE

　　B.however,

　　C.hence,

　　D.likewise,

　　这道题选项没有直接出现but选项，但是在选项里面加一个but，做题的原理还是一样。

　　but(或者这题出现的nevertheless)和however有什么区别?先看看韦氏词典解释。

　　But

　　-used to introducea statement that adds something to a previous statement and usually contrasts with it in some way

　　Nevertheless

　　-in spite of what has just been said

　　However

　　-used when you aresaying something that is different from or contrastswith a previous statement

　　注意红色部分，but(nevertheless)表示contrast(相反);however表示contrast(相反)或different(不同)。

　　举个几个例子：

　　1. MUMU喜欢胡彦斌的歌，Rebecca喜欢胡彦斌的脸。

　　2. Oliver曾经不喜欢喝咖啡，自从喝过V咖啡之后，Oliver爱上了咖啡。(让Oliver爱上咖啡的V咖啡已加入外卖，添加微信VCAFFE或者在外卖平台搜索“V咖啡”)

　　这里的第一句是different，第二句是contrast。

　　所以第一句可以用逻辑词however但是不能用but或nevertheless;第二句可以用however, but或nevertheless(词性不同，用法略有不用，这里暂时不讨论)。

　　回到SAT题，这题描述的是with sea otters和without sea otters的两种不同情况，属于different，选however;OG中还出现过的类似的对比还有用however描述白天和晚上发生的不同情况。

　　类似的逻辑词在SAT文法考试中可以分成两类：A类是but，只表示contrast;B类是however，表示contrast或different。

　　A类有but, yet, nevertheless, although despite,and notwithstanding.

　　B类有 however, while, and whereas.

　　欢迎补充指正，微信18670032014。

　　附韦氏词典解释：

　　Yet

　　-used to introducea statement that adds something to a previous statement and usually contrastswith it in some way

　　But

　　-used to introducea statement that adds something to a previous statement and usually contrastswith it in some way

　　Nevertheless

　　-in spite of whathas just been said

　　Although

　　-despite the fACTthat

　　Despite

　　-in spite of

　　Notwithstanding

　　-in spite of whathas just been said

　　However

　　-used when you aresaying something that is different from or contrasts with a previous statement

　　While

　　-used to make astatement that describes how two people, groups, ets., are different

　　-in spite of thefACT that

　　Whereas

　　-used to make astatement that describes how two people, group, etc., are different

　　-although