against的用法?

1. 反對;違反
The fight against inflation has been going on for almost two years.
抑制通貨膨脹的抗鬥已展開近兩年了。
2. 逆;對著
They sounded a sharp warning against all these tendencies.
對於這種種傾向,他們發出了嚴厲的警告。
3. 倚;靠
His desk is against the wall.
他的辦公桌靠牆放著。
4. 以...為背景
The little red house looks so beautiful against the green woods.
那座紅色的小屋在翠綠的森林襯托下顯得很美。
5. 防備;預防
We bought some warm clothes against the coming winter.
我們添置了一些禦寒的衣服以迎接即將來臨的冬季。
6. 不利於
She has said nothing against you.
她並沒有說任何對你不利的話。
7. 對比;對照
He checked the contents of the box against the bill.
他對照貨單檢查了箱子裡裝的東西。

Good decisions typically require marginal analysis that weighs incremental costs against incremental benfits 當中的against is (2. 逆;對著)

在這句中，against的意思有相對／對照／對比的意思
而整句的意思是：
好的決定基本上（典型上）需要有衡量增加的成本相對於增加的盈利的關係的邊緣分析。
其實against用作相對／對照的意思的例子很多，最常出現是我們繪圖時，就常常說A against B，如：
“Meaghan examines her demand curve for beef [x-axis product] against pork [y-axis product]. She finds that this demand curve is downward sloping.