(1)When a new movement in art (1)attains a certain fashion,it (2)is advisable to find out (2)what its advocates (3)are aiming at,(3)for,(4)however farfetched and unreasonable their principles(4) may seem today,it (5)is possible (5)that in years to come they (6)may be regarded as normal.

以上有4个从属连词+1个并列连词，因此对应有6个谓语动词。

(备注：红色为连词的所在位置，绿色为谓语动词所在谓语）

以上句子整体属于一个“并列复合句” 并列连词连接2个“主从复合句”即1个when引导为时间状语从句+并列连词for+1个however引导的让步状语从句

第1个分句为“从属连词when”引导时间状语从句

从句：When a new movement in art attains a certain fashion

结构为：when sth do sth

地2个分句为“不定式作真正主语it作形式主语的1个主句

主句：it is advisable to find out what its advocates are aiming at,

结构为：it is adj to do sth 

第3个连词for属于并列连词连接2个并列句

for+另外1个并列成分

第4个分句为”从属连接副词引导让步状语从句

从句：however farfetched and unreasonable their principles may seem today,

结构为：however+adj and +adj+主语+may+系动词seem

地5个分句为“不定式作真正主语IT作形式主语的1个主句

主句：it is possible that in years to come they may be regarded as normal.

结构为：it is adj to do sth 

When a new movement in art attains a certain fashion,时间状语从句

it is advisable to find out what its advocates are aiming at,主句（其中it为形式主语，to find out...为真正主语，what its addvocates are aimking at为不定式的宾语从句）

for,表示原因的并列连词

however farfetched and unreasonable their principles may seem today,让步状语从句

it is possible that in years to come they may be regarded as normal.主句（其中it为形式主语，that从句为真正主语从句

本句由并列连词for将二个含有状语从句的主从复合句并列，形成并列主从复合句。为了避免将for误读为however从句的一部分，for后稍作停顿，书面语中用逗号表示，以示其后的整个主从复合句是前句的原因。

试译：当一场新的艺术运动成了某种时尚的时候，我们应该明白其倡导者的意图何在。因为，无论他们的原则现在看上去是多么的牵强离奇、多么的不合理，数年之后这些原则就有可能被视为正常。