18.1.1 The referred point of time is in present tense or unknown
In all the previous chapters we had sentences, where the point of time of the narration is unknown or at least not referred to in any way (as: I thought, he said, they assume etc.). These sentences make the majority of the clauses.
He could do, whatever he wanted, nobody really cared.
We bought shirts so that we had something to put on.
You must be crazy to go out in the sun, when it is this hot.
The same applies, when there is a reference to a point of time in the present tense (meaning présent and future) as the following table shows.
Case 1: Point of narration is in present or unknown:
You smoke so many cigarettes that you will fall ill of cancer.
You have smoked so many cigarettes that you are ill of cancer now.
If you are going to smoke cigarettes, you will fall ill of cancer.