We simplify by grouping the four terms into two pairs, one concerned with the why (motivational) and the other with the how (operational). Thus each activity arises from an actual ground and has an ideal or goal. Since the activity is intentional and operative, it has direction and an instrument.
In human affairs, we can distinguish two kinds of motivational source, corresponding to ground and goal: need and aspiration. The operational sources can always be grouped according to the two kinds, direction and instrument; the former cognitive and theoretical, the latter involved and practical. Each of the six interplays has a specific interpretation. These have proved useful in understanding the scientific activity.