可以简单这样说,如Michael learns to Rock实际上它省略了how,原来应该是Michael learns (how) to Rock.Rock是动词.这是习惯性的省略,你说学游泳也可以说learn to swim.learn是及物动词,这种用法你知道它是怎样来的就行了.
为何前者的learn English的learn后面不加to,因learn是及物动词,要跟名词性的东西.
learn作不及物动词时参见下面:
v.intr.(不及物动词)
To gain knowledge,information,comprehension,or skill:
学习:获得知识、信息、理解或技巧:
learns quickly; learned about computers; learned of the job through friends.
学得很快;学习电脑;通过朋友了解那份工作