Dennis Dieks writes:

The world we perceive every day is full of things, objects, which we can distinguish from one another, follow in time, and often grasp and manipulate. This experiential fact so imposes itself on us that it is hard to imagine a world without objects. How could we reach out and make contact with the external world if there were no things to touch and see? It is no wonder, then, that from the very beginning of natural science, objects have been considered fundamental constituents of reality. It was already suggested in classical antiquity that the gross objects of our everyday experience are composed of smaller more fundamental objects and finally of smallest “atoms.” These “elementary particles” posited by ancient natural science/philosophy should of course not be confused with those of modern physics. For one thing, they differed from each other in shape and size, contrary to modern views, as we will see in a moment. The quantum theory further complicates matters and, as I will argue, makes us reject the very idea of individual particles at the fundamental level. In its place comes the image of a whole from which individual particles can emerge under special conditions.

Differences make it possible to distinguish things. If you have a number of different objects in front of you, at a certain instant, you can give them individual names; they thus have their own identity. Moreover, objects retain their identity over time, because of their different histories. Thus, if we have two distinct particles, A and B, we can after some time still identify which is A and which is B by looking at their paths in space (e.g., by filming them). So, objects not only differ at a given moment, but also possess “genidentity,” i.e. identity over time.

In classical mechanics, which got its foundations in Isaac Newton’s revolutionary Principia (1687), the concepts of “object” and “particle” play a central role. Classical mechanics is all about how distinguishable objects move under the influence of forces. Interestingly, a year before the Principia appeared, the German philosopher Leibniz (1646-1716) formulated a general principle regarding distinguishability and identity. According to Leibniz, if two things have exactly the same physical properties, then they must be one and the same thing (Leibniz’s Principle of the Identity of Indiscernibles). Accordingly, two different things cannot have all their attributes in common. Given how we conceptualize objects in everyday life and in classical physics, this seems an eminently reasonable principle. It proves, nevertheless, to be open to debate. Thus, one might wonder whether two things could share all their physical properties but yet differ in a non-empirical identity-bestowing property, “primitive thisness” or “haecceity” (from medieval Latin haecceitas, “thisness”). Such non-empirical “thisnesses” seem poorly compatible with modern scientific thinking. But the discussion has become topical again because of quantum mechanics. [Continue reading…]