I can't help but be struck by the way that Aristotle's discussion on substance has so many parallels with the "Java" computer language. In Java, an object is a data structure that represents a physical or logical entity relating to the problem which the program is trying to solve. Here are some characteristics of Java objects:

• Any given object in a Java program is itself unique, but every object is an instance of a specific class. For example, an object representing "Nick Hudson" might be an instance of the "Person" class.
• Each object has a set of properties whose values may change over the course of the object's lifetime. For example, the "Nick Hudson" object may have an "age" attribute that increases as time goes by.
• As well as being a Person, "Nick Hudson" is also an instance of any parent class of Person. This is because classes are structured in a hierarchy: for example, "Person" may be a descendant of the "Animal" class, which itself descends from "Organism", and so on. Java allows "Nick Hudson" to be referred to as either a Person, Animal or an Organism, although it is most useful to use the most specific classification.

So the Java language has analogues for Aristotle's primary substance (individual object instances), predicates (object properties), and secondary and tertiary substance (classes and parent classes). It might seem then, that Aristotle would approve of Java.

However, before any object can be instantiated in a Java program, the rules to describe the properties and capabilities of its class (and also the ancestral classes) must have already been set down. Before instantiating the "Nick Hudson" object, I must have available the definition of a "Person" class. The "Person" class acts as a kind of cookie-cutter to create each Person object. The process of instantiating each new object in Java seems more in accordance with Plato's ideas than Aristotle's.

It seems to me that Aristotle's point of view, while it may be a convincing description of how the world appears to us (what the finished program looks like when it's working), doesn't go far enough to explain how things came to be this way (where did the class definitions come from?)