从形态上看，大多数副词都是由形容词＋后缀-ly构成的，例如：slowly, heavily, truly, terribly等。
形容词变副词：
①.在形容词词尾直接加-ly。如:real-really; helpful-helpfully; careful-carefully; slow-slowly; quick-quickly; quiet-quietly
②.以辅音字母加y结尾的形容词要变y为i,然后再加-ly。如:busy-busily; angry-angrily; easy-easily
③.某些以辅音字母加不发音的字母e结尾和以-ue结尾的形容词要先去掉e,然后再加-y或-ly。如:terrible-terribly; true-truly; gentle-gently
注意: friendly; motherly; lovely，weekly，lively等词是形容词而非副词。
④.英语中还有少数与形容词同形的副词，例如：daily, early, fast, hard, high, long, near, straight, well等。请比较它们的词义和用法：
the high jump 跳高项目（形容词） to jump high 跳得高（副词）
a fast car 行得快的汽车（形容词）to drive fast 开快车（副词）
an early riser 早起的人（形容词）to get up early 起得早（副词）
a straight line直线（形容词）Go straight ahead. 一直朝前走。（副词）
注意：兼有两种形式的副词
①.late 与lately：
late意思是晚； lately 意思是最近。例如：You have come too late. What have you been doing lately?
②.deep与deeply：
deep意思是深，表示空间深度；deeply时常表示感情上的深度，深深地。例如：He pushed the stick deep into the mud. Even father was deeply moved by the film.
③.high与highly：
high表示空间高度；highly表示程度，相当于much 。例如：The plane was flying high. I think highly of your opinion.
④.wide与widely：
wide表示空间宽度；widely意思是广泛地，在许多地方 。例如：He opened the door wide. English is widely used in the world.