If you still have Cartesian-style doubts about how the physical could interact with the mental, then I suggest you buy a physical bottle of scotch, pour it down your physical throat, and wait to see if any mental changes take place.
In his ‘Meditations on First Philosophy’, René Descartes tried to answer that very question, demolishing all of his preconceived notions and opinions to begin again from the foundations.
Sure, you have your senses. But your senses often deceive you. Maybe the body you perceive yourself to have isn’t really there. Maybe all of reality, even its abstract concepts like time, shape, color, and numbers are false.
And, who’s to say you’re not dreaming? When you’re awake, you know you’re awake. But, when you’re not, do you know you’re not? How do we know that this right here is not a dream? What if you’ve been tricked into believing that reality is real? The world, your perceptions of it, your very body - you can’t disprove that they’re all just made up. And how could you exist without them? You couldn’t, so - you don’t.
Life is but a dream, and I bet you aren’t row-row-rowing the boat merrily at all. You’re rowing it wearily. Like the duped, non-existent doof you are/aren’t.
Don’t buy it? Good. Have you been persuaded? Even better. Because by being persuaded, you would prove that you are a persuaded being. You can’t be nothing if you think you’re something, even if that something…is nothing. Because no matter what you think, you’re a thinking thing.
Or, as Descartes put it, “I think, therefore I am.”
I don’t think Descartes was as smart as Leibniz. Leibniz was smarter than anybody—maybe anybody who ever lived. I don’t know about the guys on the other side of the pacific—the Chinese, the Indians—but from our guys, on our team, it’s hard to find anybody as smart as Leibniz. On the other hand, that may be why almost everything he said was false.