Causality and Change
We discussed the Law of Identity, but there are two related issues that have confused people in the past. First, it's fine to say that something exists in a particular way, but what happens when it changes. For instance, your own mind has a particular identity, but as you learn new things or direct your attention to something else, it's not the same anymore? Is it no longer the same entity? Are you no longer who you were yesterday? And the other question is how do things act and react? If I put a piece of paper into a fire, it act different from how an ice cube acts. Why? What's the nature of cause and effect?
These two concepts are related to each other, and to the Law of Identity.
Let's start with cause and effect, since it's the broader issue. Causality is the Law of Identity applied over time. What it means is that everything has an identity, and acts accordingly. If a paper is lit on fire, it burns. If an ice cube is heated, it melts. For a particular cause, there is only one effect possible for a particular entity. It's acting based on it's nature. As the ice cube gets warmer, the molecules start vibrating and it changes to a liquid state. The piece of paper is transformed through the chemical reaction brought on by intense heat, combining with oxygen particles to make smoke and ash. Given a change to the entity, the effect is based on the nature of the entity.
Sometimes this gets confused a bit. Think about bowling. You throw the ball down the aisle, and it rolls towards the pins. When it hits the pin, the pin goes flying. It's tempting to say that the bowling ball caused the pin to go flying. It's the normal way of discussing it. But in reality, the bowling ball doesn't cause something to go flying...it just hits the pin with a lot of momentum, and the pin reacts based on its own identity, and the change that's occurred. There is a necessary interaction going on, and the interaction is between two entities. The nature of the two entities, interacting together, produces the "effect" of the pin flying. Imagine if the bowling ball were made of paper. Or if the pins were made of jello. The result would be far different in either case.
Why is this important? Well, for one thing people often discuss cause and effect as if it were between two actions. The first action is the impact of the bowling ball with the pin. That's sometimes considered the cause. And the pin flying off in the opposite direction is considered the effect. But this way of expressing it makes it sound as if there is a disembodied action (the impact), which causes a second disembodied action (the pin flying). The focus needs to be on the entities interacting according to their identity, since that is the real explanation for why the reaction occurred.
It should be obvious that Change is just another aspect of Causality. An entity changes according to its identity. It doesn't just magically become something else. It follows it's identity over time. Imagine a clock with a battery. The clock hand spins around, hour after hour. There is no need for an external event...the events are internal. The change happens because you've set up the circuit and battery in an unstable state, and slowly it will correct itself, draining energy into the clock hands as they spin around. It changes because of internal causes. And we've already seen examples of change due to external conditions.
Let me just note that science is concerned with identification. It isn't primarily about determining what causes a particular effect, or how to produce a particular effect. It's concerned with identifying the specific nature of things. Part of this is understanding how it will change over time, or how it will react in particular circumstances, but these are just part of the identify of things. A science that rejects causality, or the Law of Identity, is not a science at all. If you reject that identification is possible, then whatever you happen to call science is meaningless.