I have a digital piano.
When I operate the keys of the piano (assuming it is switched on), sound comes out of the piano. When I stop operating the keys, the sound stops. If I turn off the power, the sound stops.
Now, what produces the sound? Is the sound a product of the physical piano (e.g. its circuits and speakers etc.), or could it be the product of an invisible, undetectable pixie who appears whenever the power is on a a key is pushed, thus magically generating the sound?
The answer is: it could be either or both of those things, in principle. Maybe the invisible pixie exists and is tied to the piano by a spiritual connection. Maybe when I turn the power off, the pixie is still there but it can no longer access the piano because the magical connection is interrupted. Maybe if the piano is destroyed the magical pixie will fly away to inhabit a newly-manufactured digital piano.
What I know for sure is that if I remove the speakers of the piano, it stops making a sound. If I turn off the power, it stops making a sound. If I break the circuit boards inside it, it stops making a sound. The logical conclusion I take away from that is that the speakers, the circuit boards and a power connection are all necessary to produce the sound.
I'm not so sure about the invisible pixie. When the piano is not making a sound, I find that there's always an identifiable physical cause for that (e.g. the piano isn't plugged into the power outlet). It is never the case that all physical parts of the piano are working perfectly but there's still no sound. If that happened, perhaps we could put it down to the absence of the required pixie. But it never happens.
I haven't disproved the existence of the magical pixie, you'll notice. Maybe the pixie is required for the piano to operate, and failing to turn on the power (for example) is one way to make the pixie unable to operate the piano, even though the pixie is still hanging around in the ether waiting for just the right conditions to arise to allow the pixie to make the sound. But if there is an invisible pixie, then it is clear that the piano requires both the pixie and the fully-operating physical parts of the piano. Just having the pixie by itself demonstrably won't get the job done. Besides, nobody has ever experienced a piano pixie in the absence of a piano.
So, on the one hand, we could postulate that the piano operates purely naturalistically, with the sound being produced solely by the physical components of the piano. Alternatively, we could postulate the sound is produced by the physical components and a magical pixie.
It seems to me that the simplest explanation that fits all the observations is that the sound is produced only by the physical components. The magical pixie is a superfluous hypothesis, as far as anybody can tell. If we claim we need it then we're only complicating the explanation unnecessarily. Adding the pixie to the explanation adds nothing, in terms of what we can test.
This is Occam's razor at work. Components alone beats out components plus pixie, because components alone is the simpler but equally powerful explanation.
Now think. By analogy, the human body is like the piano. The brain is like the circuit boards in the piano. The outputs of the body (the speech, the movements, etc.) are like the sound that comes out of the piano. And the soul is just like the magical pixie that is imagined by some to produce that sound: an unnecessary hypothesis that multiplies entities needlessly.
