Things change. I think we can all agree on this simple fact. Max Tegmark commented that "To me, an electron colliding with a positron and turning into a Z-boson feels about as intuitive as two colliding cars turning into a cruise ship". There are at least three ways to describe changes. Local, substantial and property changes. To illustrate, let's use Max Tegmark's example: Local change: An electron moves (changes position) from one place to another. Property change: Change in the kinetic energy (kinetic energy being a property) of an electron. Substantial change: An electron and a positron change to a Z-boson. From a Scholastic view, annihilation and creation are different kinds of processes when compared change. For example, if an electron and positron turned into a Z-boson as a result of annihilation and creation, it would look something like this: Please Register or Log in to view the hidden image! Figure 1: Annihilation and creation: The electron and positron get annihilated into nothing or nothingness and is the Z boson is created from nothing. One of the fundamental differences between these two processes (from a Scholastic point of view) is that in the case of change there is something that supports or endures through the change while remaining the same sort of thing throughout the change. For example, in local change, the location or position of the electron changes while the electron remains the same kind of thing. An electron didn't lapse into nothingness in one position and another popped into existence from nothingness at another position as that would be an example of annihilation and creation and not change. In the example of property change, the electron remains an electron and provides a "support" through the property change (e.g. kinetic energy). An electron with a certain amount of kinetic energy did not lapse into nothing and another electron with a different amount of kinetic energy did not pop into existence from nothingness as that too would be an example of annihilation and creation and not change. A property from a Scholastic point of view is described as a kind of accident. In the previous post, it was pointed out that substances and accidents are different modes of being. Like there are different kinds of substances (e.g. living and non-living), there are different kinds accidents (e.g. quantity, quality, location etc.). One important aspect is that substances are primitive when compared to accidents. Or to put it in another way, accidents "inhere" in substances. Without a substance, an accident has no real being. Aristotle identified at least nine different kinds of accidents and ever since people have tried to categorise them with some sort of system. The Scholastics and more modern attempts by Ontology research at Buffalo, the Open Biomedical Ontologies (OBO) consortium or the NCBO Bioportal ontologies tried and continue to try and incorporate some aspects of these concepts into their ontology. All this is of course very relevant to biomedical research especially related to gene ontology analyses of microarray and/or protein array expression data. The Scholastics typically divided accidents into proper and common as well as intrinsic vs extrinsic (see P Coffey. Ontology or Theory of Being) and can be summarised as follows in the following diagram: Please Register or Log in to view the hidden image! Figure 2: Accidents, a Scholastic perspective. To come back to the example of property change. Kinetic energy has both quantity (e.g. how much energy) and quality (e.g. it is a transient state of an electron). Substances are thus the substratum or underlying principle of change for accidents and accidents are composites of an accidental forms and a substance. Accidental change can thus be depicted as follows (see figure 3): Please Register or Log in to view the hidden image! Figure 3: Accidental change of kinetic energy of an electron.