Locke distinguishes the real essence from the nominal one. The real essence is some unknown insensible constitution of things on which their sensible qualities depend. In other words, it is a foundation from which all properties of things flow. For instance, the real essence of a gold ring is a constitution of its parts, on which depend all the properties of color, weight, fixedness and others. We may not know exactly this constitution of properties, but yet it is what makes the ring to be gold. In this case, this conformity of qualities to that abstract idea of gold would be the nominal essence of the ring. It is an abstract idea of the artificial constitution of genus and species.  So, the real essence of the thing is to what all properties are annexed, while the nominal essence is what gives a right to apply a thing to an abstract complex idea.

Suppose the nominal essence of man is the abstract idea into which we sorted all men. We cannot say that this complex idea of man is a real essence since our understanding of this idea depends on our knowledge of its sensible qualities. If we discover another constitution of man, from which all his sense and reason flow, we would have another idea of his essence. Consequently, our idea of any individual man would be different from what it is now.

If we take away the abstract idea of individual by which we sort all individuals, we can notice that there is nothing essential to this notion. Any faculty that an individual has can be altered by an accident or disease. His or her body may change shape and color. So, none of the faculties of an individual are essential until we refer it to some sort or species of things. It is according to this abstract idea that we suppose or speak of essential. It is in reference to the complex general idea that this or that quality of is said to be essential. Whenever we annex a particular name to the abstract idea, we know what sort of essences it stands for.

For the distinguishing beings into species, the following conditions must be satisfied. First, we must be assured that beings share certain established essences. Secondly, it is necessary to observe if these essences are presented regularly in the production of things. Thirdly, it is important to determine if beings we chose are really distinct species. Even the most monstrous productions with a particular constitution may not have those qualities which are supposed to result from the essence of that species. Finally, we ought to know the real essence of those things. We may try to frame a complex idea based on the nominal essence of beings, but we must be aware of the real essence to know all the properties that flow from it. If we do not know or know little about the real essence, then we may conclude that the thing is not of that species. It follows that we may be ignorant of numberless species since we have no ideas of its distinct properties and how they are distinguished one from another.

It is evident that the nominal essences are made by the mind and not by the nature. If nominal essences were made by nature, they would not be so various and different in all men. However, men do not make nominal essences arbitrarily. The nominal essence is a union of several compounded ideas. When the mind compounds ideas, it follows nature. In other words, men copy nature in making complex ideas out of qualities they observe. They put ideas together that are supposed to coexist. For instance, they join the voice of a ship with the shape of a sheep rather then with the shape of a horse. So, men must conform their ideas to the things really existing so that these ideas be intelligible to everybody. Though the number of compounded ideas may vary, men generally use few sensible qualities, leaving out others as material. The mind leaves out particulars of time and place, and those that distinguish particular ideas. Only ideas that are common to several sorts are left. In conclusion, nature makes many particular things which do agree one with another in many sensible qualities. It is, however, men who range these qualities into sorts for the convenience of comprehensive signs. This is how the abstract idea and the whole business of species come out.     

Bibliography:

  • Locke, John, Essay Concerning Human Understanding in Modern Philosophy, an anthology of primary sources, second edition, edited by Roger Ariew and Eric Watkins, Hackett Publishing Company, Inc. 2009