1.在情态动词后面不带： you must do as you're told 2.边迹情态助动词例如: need，dare作为情态动词后面不带to 作为主动词（实义动词）又带to。 we don't need to stay this evening.（主动词） we needn't stay this evening.（情态助动词）
3.在半助动词之后不带to：i happened to out when he called.
4.在情态成语之后：在 would rather（宁愿）、would sonner（宁可）、would just as soon（宁愿）、may\might just as well（不妨）、cannot but\cannot help but（不能不，不得不）等情态成语后面不带to不定式。 i would as soon do it by myself. 5.在would rather、would（ just） as soon 之后的than\ as-分句理解为"宁愿....而不愿意“ 这种分句不带to不定式。 he would rather listen to others than talk himself.
6.在 rather than \sooner than 之后作为”宁可.....而不“解释。 a.位于句首其后不带to不定式。rather than cause trouble，he lef. b.位于其他位置观察是否要添加to不定式使句子结构看起来更加平衡。 the manager believes it is important to invest in new machinery rather than to increase wages.
7.在主动词+主动词固定搭配的第一主动词之后 ：make believe（假装）make do （with\on）（凑合，将就，靠...维持）let drop\let fall（有意无意说出）let fly （at）（发射，发出）let slip（无意说出，错过机会）let go of\ leave go of（放开，放手）hear tell (of) (听说)，（let ）go hang(见鬼去把，不在乎) they are not rich，but they make do on what their have。
8.在make ，let ，have”使役动词“+宾语之后不带to 不定式 we can't let this go on. b.使役动词变成被动态使不带to不定式要转化成带to的不定式 john made her tell him everything= him was made to told john everything.
9. a.在感觉动词see， hear， touch， feel， watch等+宾语之后不带to不定式。 b.look at 和listen to+宾语后面也可以不带to不定式 c.被动态时候要转成带to不定式的
10.在have known +宾语之后（看过，听过）不带to不定式 i have never known =（seen）that man smile. b.被动态要带to不定式
12.在except\but之前有动词”do“的某种形式，其后通常不带to不定式 否则要带 they did nothing except work. there's no choice but to wait.
13.在”why\why not....?之后的不定式总是不带to。
