 Relying on the principle of determinability we can distinguish between the subject and the predicate of a given synthesis, e.g., in the synthesis ‘acute triangle’ we can see that ‘triangle’ can be thought without ‘acute’ but not the other way around, and hence ascertain that ‘acute’ is the predicate and ‘triangle’ the subject. Now, we can of course go one step further and try to unfold the concept of ‘triangle’. But here, the principle of determinability could assist us only to a limited degree. It will not tell us what is the genus under which ‘triangle’ falls. All it can do is to provide a negative criterion once we suggest such a genus. Thus, the principle will tell us that ‘triangle’ is not a determination of a specific figure which I see in front of me (since I can conceive of a triangle without thinking of the figure in front of me). Once I come with another candidate, such as ‘space’ and suggest that ‘triangle’ might be a determination of ‘space’, the principle will approve this suggestion, since we cannot think of a ‘triangle’ without ‘space’, though we can think of ‘space’ without ‘triangle’. This is the first main role of the principle of determinability: it assists us in uncovering the main categories of thought and their interrelations.