1. 表示“反对”，其反义词为 for。若表示“强烈反对”，一般用副词 strongly：Are you for or against the plan? 你对这个计划是赞成还是反对呢?你对这个计划是赞成还是反对呢 Public opinion is strongly against hisvisit to the country. 舆论强烈反对他访问这个国家。表示“反对”，经常同那些与之含义相关的动词连用 (如：fight, struggle, protest, argue, guard等)：The soldiers fought againstthe enemy
士兵们勇敢地打敌人。
He struggled againstthose who opposed his plan. 他同那些反对他的计划的人作斗争。

2. 表示位置，意为“靠着”、“顶着”、“迎着”、“衬着”等：The teacher’s desk is against the wall. 老师的办公桌靠墙放着。He stood leaning against the tree. 他站着斜靠在墙上。Thered flag looks very bright against the blue sky. 红旗在蓝天的衬托下显得十分鲜艳。3. 注意 against 是介词，不是动词，将其用作动词是错误的：正：I leaned against the wall. 我斜靠在墙上。正：I’m against his idea. 我反对他的意见。
误：I againt the wall. / I against his idea.