构词形态，即起构词作用的词缀变化（affixation），包括大量的前缀（prefix）和后缀（suffix）。英语的词缀灵活多变，常常一缀多义，不仅规模大、数量多，而且种类齐全。汉语利用词缀构词仍处在发展中，不论规模、数量或种类，都不及英语。

英语可以运用丰富的词缀构词造句，如：

He moved astonishingly fast.

He moved with astonishing rapidity.

His movements were astonishingly rapid.

His rapid movement astonished us.

His movement astonished us by their rapidity.

The rapidity of his movements was astonishing.(www.daowen.com)

The rapidity with which he moved astonished us.

He astonished us by moving rapidly.

He astonished us by his rapid movements.

He astonished us by the rapidity of his movements.

（他行进的速度快得令人惊讶。/他行进的速度之快，令人惊讶。/他的快速行进使我们感到惊讶。/我们对他的快速行进感到惊讶。）

英语通过词形变化，改变词性，用这些词灵活组句，可以表达一个几乎相同的意思；汉语没有词形变化，就难以用这么多的句式来表达同样的意思。英汉互译时，往往要改变词性、转换词类，才能通顺地表达原意。