1）maybe是副词,意为“也许,大概”.它通常放在句子的开头,在句子中作状语.如：
Maybe they won't come here tonight.他们大概今晚不会来这儿.
Maybe she is happy.也许她是幸福的.
2）may be是情态动词may加动词原形be构成的,在句中做谓语,意为“可能是、大概是”,后接形容词、介词短语或名词作表语.如：
She may be at home.她可能在家.（也可以说：Maybe she is at home.）
You may be right.你可能是对的.（也可以说：Maybe you are right.）
正误例析
你的钢笔可能在你的口袋里.
误：Your pen maybe in one of your pocket.
正：Your pen may be in one of your pockets.
Maybe your pen is in one of your pockets.
解析：maybe为副词“或许,可能”之意,在句中作状语；may be为情态动词may加系动词be构成,在句中作谓语,one of后面须接可数名词的复数形式.