(1) 偶然
accidental: stresses chance or unexpected occurrence: any resemblance to actual persons is entirely ~.   (chance偶然碰巧意外: determination by irrational, uncontrollable forces由无法理解不可控的力量决定)


fortuitous: so strongly suggests chance that it often connotes entire absence of cause: believes that life is more than a series of ~ events.


casual: stresses lack of real or apparent premeditation or intent: a ~ encounter of two acquaintances.   (casual还形容人穿着等随意)


contingent: suggests possibility of happening but stresses uncertainty and dependence on other future events: the ~ effects of a proposed amendment to the constitution.


accidental偶然: 强调偶发未曾预料，fortuitous完全偶然: 强烈表示偶然，甚至完全没有原因，casual偶然: 强调没有预谋目的，contingent可能: 表示有可能但不确定，取决于事态发展


记忆方法: 1) 偶然的意思是碰巧发生mean happening by chance.


(2) 次要
accidental: retains its basic notion of chance occurrence but may also imply nonessential character: the essential and ~ values of an education.   翻译成"教育的本质和非本质价值"


incidental: suggests a real, sometimes a designed, relationship, but one which is secondary and nonessential: expenses ~ to the performance of her job.


adventitious: implies a lack of essential relationship and may suggest casual addition or irrelevance: avoided elaborate designs with superfluous or ~ elements.


accidental次要偶然: 表示次要（非本质）的，但保留了偶然这一基础含义，incidental次要: 同样表示次要，但没有偶然的含义，adventitious次要无关: 同样表示次要，特别是随意增加的不相关的


记忆方法: 1) 次要的意思是非本质的mean not being part of the real or essential nature of something.