Wolff's Latin logic makes the status of concepts or Begriff much clearer than its German counterpart just by using Idea as one possible translation of the term. It is obviously ideas of Locke Wolff has in mind, which suggests that Wolffian concepts are predominantly mental images of objects. In light of this imaginative character of many of Wolffian concepts, it is evident that the already familiar classification of concepts according to their levels of clarity and distinctness need not mean to indicate that it is all about how well defined our words are. Instead, it might be all about making our mental images more detailed: if we note the way the petals of a certain rose are formed, we have made our concept of it more perfect.
Wolff reveals that the levels of clarity are actually only one way to classify concepts. Particularly, they form only a formal classification, in the sense that their difference refers more to our cognition than to the things the concepts represent. It thus appears reasonable to suppose that there are also material classifications based on the represented things and not on cognition. Before I introduce such classifications, I will have to explain Wolff's use of some concepts borrowed from ontology.
The notion of essence should already be familiar from Wolff's German metaphysics. While there essence was defined through modal notions, here Wolff explains the concept simply as the constant kernel of immutable characteristics in certain object. Although the difference is rather obscure, Wolff supposes that not all immutable characteristics are part of the essence. In addition to the essence, there are attributes – a term of Cartesian origin – which are equally immutable, but determined by the essence: for instance, if the three points of a triangle define the essence of triangles, their attributes will include at least the existence of three angles. Essence is, as it were, the basic force regulating a thing, while attributes are necessary effects of that force.
While essence and attributes are immutable characteristics, modes – another Cartesian concept – are mutable characteristics, like a colour that can be painted over. Still, modes are at least inherent to the things and not just mere relations to other things, which form then the utmost level of inessentiality and corruptibility.
Now, if some feature is mutable, it clearly cannot be used as a reliable sign for the existence of something (a red ball can survive, even if we paint it over with black). Thus, only essence and attributes can serve as characteristic marks, used for differentiating e.g. animals from one another. Indeed, we might even construct a concept that would contain nothing else but these characteristics: Wolff calls such a concept simple. Complex concepts, on the contrary, contain an abundance of characteristics, some of which are not necessary for distinguishing it from other objects (note that these characteristics need not be just modes). It goes without saying that of all perceived and imagined things we have complex concepts. Then again, all distinct notions of genera contain only characteristic marks and are thus simple (again, obscure and confused notions of genera might be complex, because they might contain characteristics not necessary for identifying a genus).
Related to the notion of complexity is the notion of concreteness. Concrete notion represents all characteristics of a thing, whether they are essential characteristics, attributes, modes or even relations to other things. A concrete notion is clearly always complex and all perceptions at least are concrete (in imagination we do not represent e.g. all relations of an apple). Then again, not all complex concepts are concrete, as the case of a complex notion of a genus testifies. If a concept is not concrete, it is abstract or represents only some characteristics of a thing, abstracted or isolated from other characteristics.
As I have already remarked, Wolff has nominalistic tendencies and he especially considers all talk of genera to be mere simplified talk of a number of individual things. A group of things share only some characteristics in the Wolffian ontology – there's no two individuals with the exactly same characteristics. Thus, fictional genera contain only some characteristics determinately. Individuals, on the other hand, must be fully determined, which is then the distinguishing characteristic of individuals for Wolff (we shall return to this point more fully in Wolffian ontology).
Now, some concepts refer to a number of objects – these Wolff calls common concepts – while others, the so-called singular concepts, refer only to one individual. As it is easy to see, an individual concept is not necessarily concrete. For instance, when I am imagining Obama, my actual mental image is an amalgamation of the actual recordings and images of Obama, but drops out some details that make perception almost perfect: still, there's only one person my imaginations are all about. Furthermore, a simple concept might also be singular: just witness the inscription ”first black president of USA”, which uses words that clearly characterize the person in question, while their combination points to no other persons.
Next time I'll discuss some linguistic matters.