What is Occam's Razor and why is it useful?
Occam's Razor is a preliminary tool of logical deduction. It states that when comparing two or more explanations for a phenomenon, the explanation with the fewest unproved assumptions is the most likely. It is useful in determining likelihood, but one should not be mislead in thinking that it points directly to the right choice. For a skeptic, Occam's Razor is about finding the most realistic explanation to favor while waiting for more information.
Here's an example:
Let's say you have to explain how the universe began. You do some measurements and calculations and discover a possible way that the universe could have begun on its own, using the existing laws of physics. You also have the alternate explanation of "god did it."
Now, let's compare these two options:
1. The theory where the universe started as a result of the laws of physics is simple, elegant, scientifically substantiated and mathematically sound. All elements of this argument are previously defined and proved. It's also falsifiable. The only thing missing is a direct observation.
2. The idea where god created the universe creates more questions than it answers. Yes, god did it, but what is god? Does god actually exist? What was god's intention in creating it? How do you prove it?
Both options explain the same thing, and are equal only because we lack a definitive smoking gun. In the future, as we learn more, this may change, but at this moment, all that matters is that either of these two answers COULD be true. We need a way to decide which answer is more likely.
Here comes Occam's Razor. Using it, we cut out explanations that introduce more questions than they resolve. The Razor favors the explanations with the fewest assumptions. Thus, option 2 is cut. WHY do we do this? Well, over history, it has repeatedly shown itself to be a reliable way to recognize bullshit for what it is. Occam's Razor predicts correct explanations quite well, too. It doesn't work 100% of the time, but it is a good pragmatic tool.
Let's look at another application of Occam's Razor:
When trying to decide between materialism (matter and energy are the only things that exist) and dualism (apart from physical matter and energy, there is also a spiritual element to the world) we have to look at the assumptions that both positions make.
1. Materialism: Currently, physical matter and energy are the only things we have proved to exist in our world with any reliability. As a result, we find no compulsion to explain various mysteries like consciousness in terms of anything except physical phenomenon. While there is no smoking gun that shows the physical structure of our brains creating consciousness, we are able to manipulate the quality of consciousness very accurately through physical means.
2. Dualism: Without a smoking gun for materialism, dualism fills the unexplained gap with a simple answer - that of a spiritual element. However, this element is not clearly defined, nor has it been measured. It is one giant assumption.
As you can probably tell, Occam's Razor clearly favors materialism because we have indirect, but measurable evidence for it, while dualism seems to only exist as an option because materialism hasn't been explicitly proved.