That's a very hard question to answer. One of the first and most important psychologists, Sir William James, defined it as "the science of mental life". But here's what I think.

Most think of our minds as a home. A free environment, like a house. That’s right, a house you grew up in. A house you know very well. So well in fact, that you know every turn of each corridor, every scratch on each wall, and every curve of each door knob. It is also a safe place, securely locked, so you are free to do what you like. It belongs to you, you and only you.

Except it doesn’t. No, I’m not saying it belongs to God. I’m saying that you forget that if you dare to go outside of the house, you’ll see a street, a neighbourhood actually. Where there are other houses, each with someone inside it. Just like yours.

We like to think we’re all different. Some parts of us are. But ultimately we all are living in the same neighbourhood, in the same houses. Just furnished differently. It's what makes us, us. But that stirs the question; how can we ever know us?

So I would like to venture outside my house. Step beyond the locked doors and look inside as many houses as possible. I don’t know why. Maybe because they’re all the same. Or maybe because they’re all different.

I know my explanation is vague. And Lord knows it's not an exact definition, but you have to give me some credit. I mean ask anyone! They'll all say it's difficult!