asleep是形容词，to be asleep等于into a state of sleep 或 sleeping，意为“睡着”，强调状态。
举例：
Is the baby asleep? 婴儿睡着了吗？
How long has he been asleep? 他睡多长时间了？
She was asleep when we walked in. 我们进来时，她正在睡觉。
asleep和fall组合，构成固定用法，等于to go to sleep，意为“睡着”，尤指“突然或出乎意料地睡着”。例如：
My grandfather was watching TV when he fell asleep on the sofa. 我爷爷看电视时在沙发上睡着了。
The moment her head touched the pillow she fell asleep. 她头一碰到枕头就睡着了。
The two girls were so tired after the birthday party that they fell asleep on the couch without having their dinner. 两个女孩生日聚会后太累了，没吃晚饭就在沙发上睡着了。
asleep是形容词，但不能用来修饰名词。例如：
She was carrying an asleep baby. （X）
She was carrying a sleeping baby. （√）
asleep用作表语不能被程度副词very或completely所修饰，而用副词sound或fast修饰。例如：
The baby is still sound asleep. 婴儿仍在酣睡。
He was fast asleep when I left. 当我离开时，他睡得正香。
sleep既是动词，也是名词。作为动词，sleep用于说明睡眠行为本身、睡眠时间长短、睡眠质量、睡觉地点或睡觉方式。例如：
I couldn't sleep because of all the noise next door. 隔壁的噪音太大，我睡不着。（睡觉行为）
He thought someone had been in the house while he was sleeping. 他认为他睡觉时有人在房子里。（睡觉行为）
Some kids sleep 12 hours a night. 有些孩子每晚睡12个小时。（睡眠时间长短）
Did you sleep well last night? 昨晚睡得好吗？（睡眠质量）
Where does the baby sleep? 婴儿睡在哪里？（睡觉地点）
Mom, can my friend and I sleep in Pete' s room? 妈妈，我和我的朋友能睡在皮特的房间吗？（睡觉地点）
How can you sleep at night with all those worries on your mind？你晚上带着那么多烦恼怎么能睡觉呢？（睡眠方式）
sleep和go, get或send组合，构成固定用法。
go to sleep表示“从醒着到睡着的过程”，意为“入睡”，例如：
He goes to sleep at 9 PM every night and wakes up at 6 AM every morning. 他每晚9点睡觉，每天早上6点醒来。
Both the children had gone to sleep when she got home. 她到家时，两个孩子都睡着了。
Go to sleep and stop worrying about it. 去睡觉吧，别再担心了。
You'll find that your baby usually goes to sleep after a feed. 你会发现你的宝宝通常会在喂食后入睡。
get to sleep表示“（设法）入睡”, 尤指受某种因素干扰很难地睡着”。例如：
Could you turn that radio down? I'm trying to get to sleep. 你能把收音机的声音关小点吗? 我想睡觉。
I didn't get to sleep until four in the morning. 我直到凌晨四点才睡着。
go back to sleep意为“（醒后）接着睡”，例如：
She rolled over and went back to sleep. 她翻了个身，又睡着了。
Go back to sleep. It's only three o'clock. 接着睡觉吧。现在才三点。
send sb to sleep意为“使人进入睡眠状态”，例如：
She brought me a cup of hot tea, hoping it would send me to sleep. 她给我一杯热茶，希望能让我入睡。
I tried to read the book but it sent me to sleep. 我试着读书，但一读就睡着了。
