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.