补上一篇的：本书把不定式也归于‘语气（mood）’类了

There are four simple moods, the Infinitive, the Indicative, the Imperative and the Subjunctive.
 

http://cs.scutde.net/courses/course_1/Grammer1/nccegram_12_subjunctive1.htm

语气（Mood）是动词的一种变化形式。它用来表示说话人对某一行为和事物所持的态度和看法。英语中有三种语气：陈述语气（Indicative Mood）、祈使语气（Imperative Mood）和虚拟语气（Subjunctive Mood）。          陈述语气：用以叙述存在的动作和状态或询问某件事情。        --Education is the best way for a nation to invest in the future.        --What wonderful weather it is!         --Have you finished reading the book?        祈使语气：用以表达请求、希望、命令、劝告、禁止等意思。        --Let’s not waste time.        --Don’t forget to close the window.        --Please tighten your safety belt.          虚拟语气：用于表示动作或状态不是客观存在的事实，而是说话人的主观愿望、请求、建议、假设     或推测。        --If there were no gravity, we should not be able to walk.        --It is important that the plan (should) be worked out today.        --If only you would listen to reason!（你如听从劝告就好了!）

 

Infinitive mood  就是 不定式