Question: How do we know we really exist and it’s not like a simulation made by our brain

Andrew McDowall answered on 27 Mar 2026:

There’s no simple answer to that, perhaps no answer at all. It would depend on your philosophical perspective. Idealism, and particularly solipsism suggests that the mind and it’s thoughts are the only things that can be known to exist. The famous “I think, therefore I am”, is proof of existance, but also the limit of absolute knowledge. Even the exisitance of your own body, your own brain to think the thoughts cannot be absolutely known. The Cheshire Cat’s smile does not need the Cheshire Cat, the smile is all there is. Nor can the existance of any other consciousness, even the one that might appear to be writing this, be known.

The counterpoint is materialism, and science in inherently materialistic. The physical world is the only true reality and all other aspects stem from it. The Cheshire Cat’s smile is a property of the Cheshire Cat. This physical reality can be observed, predictions made and tested and refined. Our ideas adapt to fit the world, the world does not alter itself to match our thoughts. This is said to be part of the development of infants – when born there is only the self, but as the child develops their inability to manipulate to the world to meet their needs and desires, particularly when the actions of other agents runs directly contrary to their wishes, leads to the acceptance of other independent agents, other selves with thoughts and motivations, and the abandonment of the of the solipsistic world view. The scientific cycle of predict-observe-modify is not inherently materialistic since it does not require a material existance and could be applied by the solipsist, but science is comunitarian, any idea must be testable and replicatable by an independent agent. If the existance of an independent agent cannot be known, then any confirmation of a concept by an external agent is actually just self confirmation by the self itself and so solipsism cannot be scientific.

The argument against materialism, against science, is that it presupposes a physical reality with defined properties. Any testing of these properties that confirms these properties is just the thought, the idea of reality confirming the rules it was created with. That if you conceive of a physical reality that cannot be modified by thought alone and then demonstrate that thought alone cannot modify it, you’re just going in circles.

Occam’s razor suggests that the simplest of two ideas with equal predictive power is the favoured explanation. Idealists believe theirs is the simpler explanation and should be prefered. Materialists believe theirs provides greater predictive powers and should be prefered. And so the argument continues…

Then there’s Dualists, who think that since both thoughts and physical reality have separate and discernable characteristics then both are distinct and both must be real. Needless to say this explanation doesn’t satisfy either the solipsist nor the materialist. One argues that physical world can’t be know, the other that the soul, can’t be separated from the body, observed and tested. Then there’s arguments over whether thoughts and the physical world are equal, or if the body is a physical manifestation of the soul, or the soul a natural expresion of a complex mind and…. anyway, it gets messy in a way that would be very familiar to medieval religous scholars.

Is there just the smile, just the cat, both smile and cat, the cat smiling or the smile catting?

Perhaps in this case it’s better to adopt the Engineer’s mindset. For all practical puposes your explanation of reality doesn’t need to be right and doesn’t need to be perfect, it just needs to be good enough and to usefully work.