Popper finds in Heraclitus more aspects of historicism that are developed later in Plato's philosophy and that have become a staple of historicist thinking.
First, historicists often confuse "legal laws or norms on the one hand and natural laws or regularities on the other" (14, 15). The laws of gravity and motion and the laws against murder and theft are not the same kind of laws. Gravity and motion are natural regularities that cannot be violated. Murder and theft are man-made conventions that quite obviously can be violated and often are. You don't have to enforce the law of gravity, but you do have to enforce the law against murder. Later in the book, Popper will suggest that we call natural laws laws and legal laws norms. Can you think of examples in current debate where people confuse natural laws and legal norms?
This confusion often leads historicists to uncover the laws of change, which they will often talk about as if they were natural laws and not man-made norms. Thus, Karl Marx might talk about the laws of economics which were at work to bring about the inevitable victory of the working class in the perfect communist state. Can you think of any laws/norms that people claim today are driving the way society works and history is unfolding?
Then, Popper notes that "historicist ideas easily become prominent in times of great social change" (17). It seems that when life becomes unstable and threatening, then people want the reassurance of reliable laws that will inevitably return life to a more stable, secure, and pleasant Golden Age. Can you think of any instability in current life that prompts people to seek haven in a set of laws that promise stability and security? Let us know.