So, for Piaget, there were four distinct stages. The first is the sensorimotor stage. This is the initial stage, and runs for about the first two years of life. At this stage, the baby is a purely sensory creature. Information is gained through the senses and through the child's motoric activities. But the child perceives and manipulates, but doesn't have any reasoning. There's no sense of time, no sensors stability, not even a differentiation early on, between the child and other people. It's at this stage over a lengthy and interesting process, that object permanence is attained. What object permanence is, is the understanding that objects exist independently of one's actions or perceptions of them. So, if I have a ball and I put it behind a screen, you know even though the ball is at a site, that it will continue to exist. This might seem so obvious, it's barely worth saying. But Piaget's claim was, that before about six months of age, babies act as though objects remove from site are gone. They're so caught up, in the sensation, in the here and now, that they lack the ability to appreciate object permanence. For instance, this is why according to Piaget, babies are so amused by peekable. You cover up your face, and then reveal it, and then babies crack up or gasp and surprise or whatever, and it's because when you cover up your face, they think you're gone. Then when you open it up, you reappear, which is amazing. So, that's the first stage. The second stage, which has been the subject of most psychological development on research is age from 2-7. The baby is now a child and starting to reason. They have object permanence, they have other capacities, they can think, they can differentiate themselves from others, they have a rudimentary understanding of time, but they have certain very interesting limitations. They can reason, but they can't reason into higher order away that you and I can. One illustration of this, is what Piaget called egocentrism. So, children are egocentric. He didn't mean this in a way that when I say oh, my best friend is egocentric. Meaning he cares only for himself, doesn't care about other people. What Piaget meant was, children literally can't see the world through another's eyes, they literally can't understand that other people have different perspectives than they have. So, one classic illustration of this, is the Three Mountains task. Into Three Mountains task, the child is put in a position where he looks at three mountains of different heights in different orientations, and he's asked to draw it. For instance, he could draw it pretty well as a kid a four or five year old. But now, he's asked, "How would somebody who's on the opposite side of the stage draw? Who sees it from a different angle." At this point in development, children according to Piaget, they are just incapable of understanding other people who have different perspectives and draw the mountains in different ways. They believe other people draw the mountains as they do. In general, Piaget believed that for children, they didn't quite get the idea that they could know something and another person couldn't know it, or that other people could know things that they don't. They are egocentric in that they think the world as they see it, is pretty much the world as everybody else sees it. That's our first main limitation. The second main limitation, is according to Piaget, they lack the concept of conservation. What conservation is, is the idea that certain operations on the world will change some properties but not others. An adult appreciates that the number of things will remain constant even if you move them around. If I have a bunch of checkers and I slide some of them to make them take up more space and they say, "Are there more checkers here?" You'd laugh and say, "Of course not, they're just spread out". But kids can't conserve a number through a transformation, and so they think that there are now more. Similarly, if you pour water into a container that's every different shapes or the water that becomes higher or takes up more space lengthwise or something. For an adult, is the same amount of water, volume of water is conserved across the transformation, but for kids, you put water into a tall glass and say, is there are more now, and they I'll say yes. There's a lot of findings of Piaget that you could really question, and are very critical. We'll get to some of that. But I'll tell you, this is really cool, you can really do this if you have a kid. So, for instance, you could do make the stakes count. You have some M and Ms, that you have some M and Ms, any kid has M and M's and you say, "Who has more and which ones do you want?" The kids might count and say, "About the same". Then you take one pile of M and Ms and you spread them out and now you say, who has more and because I want the ones that are spread out because now there's more, which is kind of nuts. The next stage around age seven, is the concrete operational stage. At this point, the kid is pretty sophisticated. You have less egocentricity, more logical thought, you don't have problems with conservation. But still even at this point, there's an inability to reason fully abstractly or fully hypothetically. One way to put it, is the child isn't quite capable of scientific reasoning at this point. But here's an example, suppose all of a sudden I had back pain, and driving it why don't I have back pain. So, I might do experiments. I might say, "Well, maybe I should flip my mattress," see how that makes me feel. Or I change my shoes or maybe I'm lifting firewood too much, you can experiment. You do, and we do this all the time. When we think about experiments, we think that's something which scientists doing laboratory. But in real life, we often do experimentally, I'd figure, why is our car making this noise? May be able to change the type of gas, you put into it or maybe I'm riding to break too heavy. You try out different things and you make generalizations and so on. This reasoning might come naturally for sophisticated adult, but is not present at this early stage. So, children struggle with it. Finally, you become an adult. You enter what's called a formal operation stage where you are a full-fledged adult. Unlike Freud, Piaget didn't believe that there were further traumas, or troubles, or developments, or transformations as an adult. He believed everybody went through these stages. He was rather mellow about them, often he would give lectures in the United States, and he described the American question as, "How do you speed up these stages. I want my kid to get formal operations at age 10". But overall, Piaget say that these are just a natural stage that the mind goes through. Developing over time through experience and through cognitive restructuring, to bring it from a baby who has an extraordinarily limited understanding of the world to us, who are pretty damn smart.