A difficulty with psychology is that everything is so hard to define.
You think. You know the experience of thinking, how it is to have conversations in you head, how it is to visualize places and timelines in the inner space behind your eyelids.
This is an “ability” that you have, and that is also recognized by your friends and family. We, humans, understand this experience. We are not sure how far animals or plants or other creatures can do it, but we know we do it.
If it’s an ability shared among us, then there’s an apparatus within us that makes it possible to happen. I am giving this “apparatus” a name. I am calling it your “mental system” or simply — your “mind”.

Now that we gave this experience a name, I hope it becomes clearer to you that
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Just like you are not your brain, your arm, your vision, your digestion, your metabolism — you are not your mental system.
(I’ll keep repeating this throughout this map. You’ll notice why.)
You “use” your mind to produce thoughts. In practice, this is what it looks like: