In the formal operational stage, children are able to think about abstract ideas. The abstract ideas are ones that are within the child’s mind and not in front of them in the world. In this stage, children can come up with rules about how things can happen without needing concrete items. Piaget believed that there were two main parts of the formal operational stage: hypothetico-deductive reasoning and propositional thought. In hyothetico-deductive reasoning children are able to guess the outcome of a problem. They are able to do this by making guesses that can be tested in an experiment. By testing the guesses they learn if their guess was right and if not why it was not. In propositional thought children are able to understand if spoken statements are true. They are able to do so without needing to see an example of those statements.