一、usually,sometimes,always,often等词在英文中被称为“频度副词”,是用来表示动作频率的,但程度上有别.一般说来可按频率大小排列：
always＞usually＞often＞sometimes＞seldom（很少）＞never（决不）
二、频度副词的位置
1.在be动词之后.如：She is sometimes very busy.她有时很忙.
2.在第一个动词或情态动词之后.如：
I will never forget the first time I met you.我将永远忘不了和你的第一次见面.
3.在实义动词之前.如：
We often go there.我们常去那儿.
4.sometimes也可放在句首、句中或句末,often也可放在句末.如：
Sometimes she writes to me.她有时候给我写信.
She writes to me often.她经常给我写信.
三、用法
1.often,always,usually等通常和一般现在时连用,表示现在经常或反复发生的动作.如：
It often rains here in April.这儿四月份常下雨.
2.always与进行时连用时,并不强调动作正在进行,而是表示赞叹、厌烦等情绪.如：
He is always thinking of others.他总是想着别人.（赞叹）
She is always asking silly questions.她老是问些愚蠢的问题.（厌烦）
3.对这些频度副词提问时,用how often.如：
I write to my brother sometimes.
How often do you write to your brother?
英语中always,usually,often,sometimes,seldom,never等,叫做频度副词.这类词用来表示某一动作发生的频率,或某一状态出现的频率,即在一定的时间内动作重复发生或状态重复出现的次数.如：
I always work hard at English.
I usually go to school at seven.
Do your friends often write to you?
Sometimes they play football on Friday.
He is seldom ill.
He never tells a lie.
上述副词表示的频度,虽然在意义上所差别,但它们在句中的位置却基本相同.
现将它们在句中的位置归纳如下：
一、如果是to be句型,频度副词要放在to be的后面.例如：He is often late for work.
二、如果谓语动词是实义动词,那么频度副词常常放在它的前面.例如：
I usually watch TV at seven in the evening.
三、如果句中含有情态动词或助动词,频度副词要放在它们的后面.例如：
He can often help you.
His father doesn't always watch TV in the evening.
四、sometimes还可放在句首或句尾.例如：
Sometimes we read English under the tree.
We go to work in a factory sometimes.
always(100%) usually(80%) often (30-50%)
sometimes(20%) hardly ever(5%) never(0%)