obstinate: implies usually a perverse or unreasonable persistence: a President who was resolute but never ~.  （perverse反常有悖常理what most people think is wrong, unacceptable or unreasonable, 如a perverse decision有悖常理的决定，又如sexual perversion性变态）


dogged: suggests a tenacious, sometimes sullen and unwavering, persistence: pursued the story with ~ perseverance.  （tenacious紧抓不放的，TEN词根表示hold抓住，如tenure任期表示"hold抓住"职位，又如hold onto your dream like a dog with a bone像狗咬紧骨头一样抓住梦想，形象的说明了dogged和tenacious意思相同，谚语it's dogged that does it天下无难事只怕有心人）   （sullen不吱声不交流不合作，如remained sullen throughout the party整个聚会一言不发）  （waver动摇,指做出决定后又开始犹豫to hesitate after seeming to reach a decision,如wavered in his support of the rebels对叛军的支持动摇了）


stubborn: implies innate sturdiness or immovability in resisting attempts to change or abandon a course or opinion: swallow your ~ pride and admit that you are wrong.   （sturdy结实健壮不易损害strong and not easily injured or damaged,如a sturdy table结实的桌子）


pertinacious: suggests an annoying or irksome persistence: a ~ salesman who wouldn't take no for an answer.  annoy和irk都表示让人讨厌，irk还表示不耐烦


mulish: implies a settled and thoroughly unreasonable obstinacy: a ~ determination to stick with a lost cause.  settled: 稳定的; 不大可能改变的  mule骡子,顽固的人    


这组词意思都是顽固，obstinate: 表示反常不合理的坚持，dogged坚持不懈: 表示紧抓不放,不吱声不动摇,本组唯一褒义词,用狗比喻很形象，stubborn: 指生性顽固不化(innate sturdiness, immovability)，拒绝改变放弃，pertinacious: 表示让人厌烦的坚持，mulish: 指完全不合理反常的坚持


记忆方法: 1）首字母ODSPM, Prime Minister DOS首相做事<==顽固      dos and don'ts做的事和不做的事，即注意事项准则，如he always dressed badly, like he's got no idea about fashion dos and don'ts他穿着没品味，好像不知道穿衣注意事项

         2）练习一下

         3）顽固的意思是做事固执不让步(settled,unyielding)mean settled and unyielding in an course or purpose.首字母ODSPM, Prime Minister DOS首相做事<==顽固