The hypothesis of the existence of three different quarks with specific properties of their own, was put forward in 1962 by Murray Gell-Mann. The extraordinary thing about quarks is that they should have a completely different electric charge. [北大《英语》(三), p. 108]
[原译]存在三种不同的,各有特色的夸克这个假说是格尔曼在1962年提出来的。夸克异乎寻常的地方在于它们可能带有完全不同的电荷。(教参)
夸克仅仅“可能带有完全不同的电荷”，怎么就会成为“异乎寻常的事”呢？请分析。
请注意在上例中,should的情态意味并不是“可能”,而是:作者由于出乎意料之外而感到惊奇。这种用法的 should 可以翻译成“竟然”“居然”,也可以不翻译出来。类例:
-
It is most unreasonable that he had won her heart and should have jilted her soon afterwards. 在他赢得她欢心之后，居然很快就抛弃了她，这真是太不合理了（should 表示出乎意料之外和不满）。
-
It's wonderful that you should have achieved so much in these years. 这几年来你们竟取得了这么大的成就, 真了不起 (should 表示意外和赞叹)。
-
Strange that I should have forgotten its name! 说也奇怪,我竟然忘记了它的名字 (should 表示婉惜、遗憾)!
-
It's unthinkable that he should be so foolish. 他居然这样愚笨,真是不可想象(should 表示意外和吃惊)。
-
That such a change should have taken place was incredible to him. 竟然发生了这种变化,对他来说是难以置信的。
-
It is hardly credible that time should have passed so quickly. (DEU) 时间竟过得这么快, 简直难以置信。