By A is meant B^★
 【问】 By the skill of reading is meant what is generally known as reading comprehension.
 我认为介词短语by the skill of reading是句子的主语①，不知对否?
 【答】 在By A is meant B这个句型中，B是被动句的主语，而by A(介词短语)是状语。这个句型常用来给事物下定义。A是被下定义的部分，包含已知信息，而B是下定义部分，即揭示概念内涵和(或)外延的部分，当然是要告诉读者的新信息。采用这种倒装语序，就能使新信息
 (即语意重点)位于句尾这个被强调的位置上(见end-focus)。原来这是个强调被动句主语的随意的语用用法，久而久之，便成了固定的语法格式了。在英语论说文和科技英语中用得非常广泛的。例如：
 1. By acceleration is meant the rate of change of velocity with time.
 加速度就是指速度对时间的变化率。
 2. By power is meant the rate of doing work.
 功率就是指做功的速率。
 3. By motion here is meant momentum.
 这里所说的运动指的是动量。
 4. By automation is meant the technique of making a mechanical device or a process self-regulating and self-controlling.
 自动化是指能使机械装置或操作过程进行自动调节和自动控制的技术。
 5. By “strategy” is meant the basic planning of the whole operation. (CGEL)
 “策略”是指整个操作的基本计划。
 请与下列主谓倒装的被动句进行对比：
 1. In each phenomenon there is involved some change in energy.
 在每种现象里都涉及到能量的某些变化。
 2. To every action there is always opposed an equal reaction.
 对于每个作用力总存在一个大小相等、方向相反的反作用力。
 3. Whenever any positive charge is created，there is always created an equal amount of neg-ative charge.
 每当正电荷产生时，总有等量的负电荷产生。
 4. By degree of freedom is understood an independent variable quantity，such as pressure，temperature or concentration.
 所谓自由度，乃是一个独立的变量，如压力、温度或浓度。
 (上列各句中的主语也是被强调的成分，是句子的语义重点)
 (参见《现代外语》1983年第5期上拙文《科技英语简单句的语序与强调》)