maintain: stresses firmness of conviction, and is likely to suggest persistent or insistent upholding of a cause and may suggest aggressiveness or obtrusiveness: steadfastly ~ed his client's innocence.    （aggressive强势，有侵略性an aggressive executive一个强势的经理，obtrusive突兀扎眼an obtrusive manner突兀的行事，maintain强调坚持，未必强势突兀，因此中文解释没有采用这两个词）


assert: suggests a determination to make others accept one's claim of one's position: fiercely ~ed that credit for discovery belonged to her.        （claim宣称某事，或者某物属于自己to say something is true, or belongs to that person，如机场提取行李处叫luggage claim）         (position观点意见，专指有分歧的观点where there is a difference of opinion，如the candidate discussed his position on the war候选人论述了他对战争的观点)


defend: implies maintaining one's claim in the face of attack or criticism: I need not ~ my wartime record.


vindicate: implies a successful defending: his success ~d our faith in him.       他的成功证明了我们对他的信心(信念)，faith信念是指即使在没有证据的情况下仍然相信，因此比信心更坚定


justify: implies a showing to be true, right, acceptable, or valid by appeal to a standard or precedent: threats to public safety ~ied such drastic steps.


maintain坚持: 强调坚信，指长时间地支持某种观点或行为，assert坚称: 表示坚决地宣称自己的不同观点，defend辩护: 特指在面对批评攻击时坚持观点，vindicate证明: 表示成功的辩护，justify也是证明:  证明某事真实正确有效，因为符合标准或先例经验


记忆方法: 1）首字母首字母MADVJ想成MAD JV疯狂的合资<==坚称       joint venture合资公司,如空客、一汽大众   

               2）坚称的意思是坚持认为真实正确正当合理mean to uphold as true, right, just, or reasonable.    （uphold表示支持support given to something, 特别是面临批评置疑时的支持especially something that is attacked，如the President upheld the legitimacy of the military action总统支持军事行动）