想当然的英文：
assume sth. as a matter of course

参考例句：

Don't take it for granted.
不要想当然

We must not act on assumptions.
我们不能凭想当然办事。

We must not act on assumptions.
我们不能凭想当然办事。

Mr. Wang also stroked his mustache and repeated Su Tung-p'o's famous line, Most certainly!Most certainly!'"
汪先生也摸着胡子，反复援引苏东坡的名言道:“‘想当然耳’，‘想当然耳’哦！”

assume是什么意思：
v. 假定；臆断；采取；承担；呈现；夺取，继承；装腔作势

The responsibility for the accident was assumed by me.
事故责任由我承担。

To state or assume as a proposition in an argument.
假设，预设命题在论证中做为一命题陈述或假设。

take up (=assume) this mission
承担这使命

sth是什么意思：
abbr. something的缩略词

average sth out(at sth);calculate the average of sth
算出某事物的平均数

be agreeable to sth
欣然同意某事

at/on the altar of sth
因为，为了（值得为之受苦的事）

matter是什么意思：
n. 物质，事情，素材
v. 有关系

be of importance;matter
有重要性;有关系

It is no laughing matter.
这没有什么可笑的。

deposited matter
沉积物|沉淀物