Spinoza: ‘A true idea must agree with that of which it is the idea [ideatum]’.
Maybe this condition leaves the true idea in a state of impossible validation, since it seems impossible to determine what is the ideatum of an idea from elsewhere than from the idea itself.
However, if we test the hypothesis of an idea that not agrees with its ideatum, we will find that the disagreement can be revealed.
The disagreement involves definite positions for the idea and its object or ideatum, so that we may compare them as self-subsistent entities.
As a paradox of knowledge, we cannot appreciate plainly the character of the object that belongs to a false idea. Yet, that object receives rough outlines from the false idea itself.
There are blatantly false ideas or genuine false ideas with many credentials for being accepted as true ones. What makes the first blatantly false is their reference to things that do not require an investigation of their truth. Their falsity is, therefore, easily imputable to their author and the falsity becomes a simple error.
Meanwhile, the genuine false ideas are those that suggest they used for their construction the participation both of the author and of their objects. And such supposition is grounded on the possibility of giving to their objects definite names. A definite name is one bearing a greater sonority than others and keeping it in itself; for instance, the names of the scientific matters – a catalogue of scientific labels of some studied things becomes easily convincing in virtue of its firm sonority and makes impossible to perceive the things otherwise than through their names. Since we know that things cannot be confounded with their names, the self-indulgence of the authors of ideas in naming things is a sure sign that their ideas do not agree with their objects.
Conversely, an idea that use weak names for its object point to the fact that it is in agreement with it. The so blamed metaphysical concepts as being, one, substance seem suitable for being considered as forming ideas that use weak names.