So, if you're being observant here, you'll notice there's a bit of a problem. I just talked about all the evidence that babies have powerful knowledge of the physical and social world, but what about the PHAD and observations? I also talked about all of these studies finding that kids get it wrong, that kids think differently about the world, like kids don't understand certain things that come naturally to adults. In any adequate theory of development has to explain what kids know and what they don't know. Also, there's other work since PHA finding some really interesting limitations on the part of children, and in particular on the part of children's social reasoning. So first, I'm going to show you this film clip that dramatically illustrates a way in which kids are just different from adults. Watch this wonderful example with psychologists Joan Pascal and three-year-old, Jacob. You're going to choose one of the stickers and he's going to choose one of the stickers, but he always chooses first and he always wants the one that you really want. He doesn't care if you're sad. Let's put monkey into another room so that he doesn't know which sticker you really want. You tell me, which sticker do you really like? Which sticker do you not want? Now I'm going to bring back mean monkey, and he's going to choose first. Remember, he always wants the sticker that you really want, he doesn't care if you're sad. So think of what you can do or say so that he doesn't get the one that you really want. Here comes mean monkey. Which sticker am I going to choose? Jacob, which sticker do you really want? Oh, well then I'm going to take that one so you get to take this one. Joan repeats the experiment several times with each child, giving them ample opportunity to deceive the monkey as to what they really want. Tell me which sticker you really like. That one. Which sticker do you not want? That one. Okay. Jacob, which sticker are you going to take? Well then, I'm going to take that one, and you are going to have this one. Bravely accepting, three-year-old Jacob never figures out that the monkey can be fooled. But what about Patrick, 18 months older, and already with a knowing gleam in his eyes. So that he doesn't know which sticker you really want. Which one do you really like? Point to which one you really like. That one. Which sticker do you really not want? Which is a yucky sticker? That one. Okay. Well, leave those stickers there I'm going to bring in mean monkey. Let me see which one I want. Patrick, which one do you really like? Oh, well, then I'm going to take that one and you get to have that one. I had my fingers crossed. Patrick has also crossed the threshold into the adult world. He's now old enough to know that he can think things that others don't, that his thought are his alone. From about four and a half to five, they suddenly and rapidly get that knowledge. They begin to think about other people's thoughts. They begin to think that somebody can think something different from what they know, that people's thoughts very are private and maybe incorrect. People can have false thoughts about something that they know to be true. Once you understand that, then you can explain all sorts of things about why people do things which seem strange to you. They're looking for things and you know that that's not where they are. It also means then that you can understand how to surprise people, how to trick people because once you've met the split between the mind and the world, then you can think about people's minds and manipulate the way the world is, so that they come to believe certain things about it. We'll take this classic finding, and this is one of the major findings in development of psychology, one of the most interesting discoveries of the difference between children and adults. The gist of this is that up until the age of about four or five, children don't understand something really important about the minds of other people. They don't understand that other people can have false beliefs. So to test this, this is one classic task that explores this known as the Sally & Anne test. So, I'll walk you through it. We'll pretend that you're a child, I'll walk you through it. So first I introduced you to the characters. This is Sally. Sally has a basket. This is Anne. Anne has a box. Sally has a marble and Sally's going to put it in the basket. There's Anne, Anne's watching her put into the basket. Then Sally leaves. Then Anne gets up, takes the marble out of the basket and puts it in the box. Now Sally returns and she wants to play with her marble. So question, where will Sally look for her marble? Now, I bet what you will say being a sophisticated neurologically intact adult is, ''She'll look in the basket, that's where she put it.'' But kids don't say that. Kids say, she'll should look in the box because that's where it is. More generally, children have a lot of problems realizing that other people could have beliefs about the world that are false. This is something which really does need to be explained.