The first action (“he has agreed to help me”) is in the present tense (perfect aspect) while the second (“so I was not doing homework”) is in the past tense. The same is true for the second action. What is your second sentence about? In both sentences, the first action must be either in the simple past or the past perfect if the second action is in the simple past. that’s the sequence of tenses rule. If the first action is in the present perfect, the second action can be in the future (“will not do.”). Why I said cause-effect relationship is that it puts the cause (first action) first and the effect (second action) second, which is the sequence of events. The sequence of tenses must reflect the sequence of events. What is the cause and effect relationship between an event and the individual events that caused it? All that is important is that one issue followed another in time: that establishes a sequence of events that must be reflected in the sequence of

tenses.