虚拟语气（1）
一般来说，在科技文中，虚拟语气主要用于以下三种情况： （1）与事实相反、或不可能实现、或难于实现的事。 （2）表示主观愿望、要求、建议、命令等。 （3）表示语气委婉或主观的推测。 一、科技文中虚拟语气的主要形式 1、条件式虚拟语气：这属于上面提到的第一类虚拟情况。它一般用于表示与事实不符、不能实现或难以实现的事。根据假设条件所涉及的时间，它又可分成三类，现列表如下（均以主动语态为例）：
假设时间 条件句中的谓语 主句的谓语 涉及现在或将来 过去时(be用were/was) 过去将来时(should/would/could +…) 涉及过去 用过去完成时 过去将来完成时 （had + 过去分词） (should/would/could+have+过去分词) 涉及将来 1、 { (should+)动词原形 } { 过去将来时/一般将来时/一般 现在时[有时是可能实现的，这时一般表示委婉、推测或告诫]} 2、 {were + 动词不定式} {对于不易实现的事用过去将来时} (“万一；一旦；若要；如果) 注：在“涉及将来”的条件从句的第一种情况，一般说来英国人用“should”而美国人则省去“should”，而在书刊中出现的多数情况是采用美国式（但如果省去“if”的话，英美人都得把“should”放在从句的句首）。
(1)涉及现在 If it were possible to divide(分割) the magnets(磁铁) until we reached (到达) the molecules(分子), we should find (发现)each molecule to be a magnet. If there were a gas(气体) that did not liquefy(液化) before reaching 0oK, at 0oK its volume(体积) would shrink (缩小) to zero. If friction(摩擦) could be eliminated (消除), no force at all would be necessary to keep(保持) the book in motion, once(一旦) it had been started (启动). If the circuit(电路) be purely(纯) resistive(电阻性), XL would be equal to XC.
(2)涉及过去 It would have taken them a long time to solve(解) the complicated(复杂的) problem (题) if computers had not been used. Similar formulas(类似的公式) could have been obtained (得到)if we had started with(以…开始) partial derivatives(偏导数) with respect to(相对于) x or y.
(3)涉及将来 If the orbital motion(轨道式运动) of the earth were to cease (停止)it would fall toward the sun. If the pressure(压力) (should) be raised (提高)further(进一步), the container (容器)will break(破裂). 注意： ① 在汉译含有虚拟语气的句子时，绝不能按时态的本来含义进行翻译。这些时态仅是借用来表示虚拟语气的。
②“if”条件句中若有“were, had, should, could等”这类动词时，从属连接词“if”可以省去，这时从句要发生部分倒装现象（其倒装方法与构成一般疑问句类同）。 Were the wire(导线) of a small diameter(直径), its resistance(电阻) would be increased. Could a pin(大头针) be drawn(拉) into a wire(细丝) of the thickness(粗细) of one atom(原子), it would encircle (绕) the earth thousands of times(次). We would have obtained a positive current(正的电流) had we assumed (假设) the opposite(相反的) direction. Should these bombers(轰炸机) encounter (遇到)such an air-defense system(空防系统), the results(后果) could be fatal(致命的).