Monism (from the Greek word monos, meaning “single” or “alone”) is the view that everything is ultimately one. Nothing that exists is really distinct from anything else that exists—which is just to say that, in the final analysis, only one thing exists. And that one thing—call it “the universe,” “reality,” “the One,” or whatever you like—cannot be divided or decomposed into more fundamental parts or constituents. If it could, then reality would not be ultimately one. It would be ultimately many.
So the Monist has to say that the apparent diversity we experience in the world is an illusion. The distinctions we make between things are only in our minds, because if those things were really distinct from one another, there would be more than one thing in existence.
Monism is a very radical philosophy. It has generally proven more popular in Eastern philosophies and religions than in Western ones. While it has enjoyed some sophisticated defenders over the course of history, it faces some quite formidable objections.
In the first place, Monism is highly counterintuitive and flies in the face of our immediate sense experience. It asks us to disregard as illusory one of the most basic features of the world as it appears to us. It implies that our experiences of the world are thoroughly unreliable. After all, those experiences present us with a plurality of things: people, cats, dogs, trees, cars, doughnuts, cell phones, and the like. For the Monist, all these diverse things are either ultimately identical or ultimately unreal. Neither of these options is easy to swallow or to defend.
What’s more, it’s tough to live as a consistent Monist. Our everyday thoughts and decisions presuppose real distinctions between things: between your body and my body, between your spouse and my spouse, between your car and my car, between your credit card and my credit card, and so on.
And what goes for physical things such as our bodies must go for non-physical things such as our minds, as well. If Monism is true, your mind must be ultimately identical to my mind; your thoughts must be ultimately identical to my thoughts. But in that case, how could we disagree about anything? For example, how could we have different thoughts about whether or not Monism is true?
Here’s one final question to ponder: Was your answer to the Unity Question consistent with your answers to all the earlier questions? Recall that you answered yes to the Truth Question, yes to the Knowledge Question, and yes to the Goodness Question. Those answers indicate that you believe in distinctions between truth and falsity, between knowledge and ignorance, and between goodness and badness.
Can a consistent Monist accept that those distinctions are real?
(from James Anderson's "What is Your Worldview?")