Note that a variable may be both an X v and Xs in a specific case. Our H specifies some relationship between two standards. These scales are important and differ in important ways, but present little difficulty with respect to the immediate discussion. Ice melts at Ooc. Taller people weigh more h.
Richer people have more money.
Note that the sequence could be reversed, but adds no additonal variations. This, again, should not discourage you. You may be interested in more than one H, and you may want to actually do your research on several H's with more than two variables, but you will find it easier to work on them one at a time, and then combine them. In principle, at least, any assertion can be in this form, and, in research, formulating hypotheses is a characteristic, if not also required, part of the process. It should also be clear that these are not two mutually exclusive categories but are, in the extreme case, the end points of a dimension.