To express past expectation and assumption, the same auxiliariesA helping verb used with main verbs to express mood, voice and tense. E.g.: I can't stand when I am disturbed. ("can", "am") are used in the case of present expectations and assumptions. However, the infinitives that follow are perfectThe aspect expressing completion. E.g.: He’s finished university. infinitives.

To express prediction, expectation and assumption, the following auxiliariesA helping verb used with main verbs to express mood, voice and tense. E.g.: I can't stand when I am disturbed. ("can", "am") are used.