Conjectures and Refutations: The Growth of Scientific Knowledge (1963) is a work of nonfiction on scientific knowledge and discovery by Karl Popper. The book posits that the fundamental difference between science and pseudo-science is falsification, the process of using rigorous and empirical tests to evaluate a theory’s credibility. This was a great departure from previous explanations of the scientific method’s unique ability to understand the world, as philosophers had previously theorized that empirical observation and verification were the basis of the scientific method. Popper instead suggests that neither empiricism nor pure reasoning are the basis of human knowledge, as neither on their own can truly evaluate the validity of a theory. He argues that it is only through a process of trial and error, and through the rejection of falsified theories, that people can be certain they are working toward a greater truth.

Conjectures and Refutations received critical acclaim upon its publication and has been considered a fundamental text in the fields of philosophy and science ever since.

This guide uses the 1963 first edition published by Basic Books.

Summary

Conjectures and Refutations includes 20 chapters divided into two segments. The first, titled “Conjectures,” includes the Introduction and Chapters 1-10. The second, titled “Refutations,” covers Chapters 11-20. Broadly speaking, the first segment defines Popper’s falsification theory and provides a historical overview of the European development of the philosophy of science from Ancient Greece to the modern era. The second segment discusses Popper’s critical rationalism in contrast with competing philosophical ideas, such as instrumentalism and relativism. It also provides greater insight into Popper’s liberal political and social outlook, which is an extension of his rationalism.

Chapters 1-5 of “Conjectures” discuss Popper’s falsification theory in relation to recent trends in the field of the philosophy of science. Chapter 1 explains how Popper first began questioning the explanatory power of science and how he stumbled upon the concept of falsification. Chapter 2 is a commentary and criticism of Ludwig Wittgenstein’s thesis on the futility of philosophy. Popper maintains that philosophy should not be disregarded as an absurd pseudo-science, so long as it continues to engage in genuine questions and produces falsifiable theories. Chapter 3 is a historical overview of the ancient Greek tradition of critical discussion, which Popper believes is the key to the great scientific revolutions of the Enlightenment era and beyond. Chapter 4 defends the utility of tradition in the development of science, despite the popular opinion that traditions are to be destroyed for being based on myths. Chapter 5 discusses how the Pre-Socratics welcomed criticism and practiced falsification in their intellectual method. Popper claims that this led to great scientific discoveries and should be part of the modern-day scientific work ethic.

Chapters 6-10 of “Conjectures” continue to provide insight into questions of epistemology by discussing the existence of objective truth—that is, a reality outside the realm of human experience. Chapter 6 is a brief note on the work of philosopher George Berkeley. Chapters 7 and 8 use philosopher Immanuel Kant’s work to explore the topics of empiricism and pure reason. Popper argues that while objective truth cannot yet be proven to exist, the ability to use empirical evidence and reasoning to falsify a theory implies that some scientific ideas are more accurate than others. In Chapters 9 and 10, Popper uses logical reasoning to prove that degrees of verisimilitude exist, and the greater the content of a scientific prediction, the riskier it is, and the greater the insight it can provide into the true nature of the world.

Chapters 11-14 of “Refutations” explore the role of language in the quest for truth. In Chapter 11, Popper critiques linguist and philosopher Rudolf Carnap’s project for building a scientific language devoid of meaninglessness. Popper claims that it is unnecessary to build a different linguistic system for science, as oftentimes seemingly meaningless sentences still serve a function in the process of falsification. Chapter 12 expands upon this idea by exploring the four major functions of language, with Popper arguing that they convey thoughts and ideas and entice discussions. A language need not be perfectly “objective” or devoid of “useless words” to convey meaning. Chapter 13 is a reply to Professor Wilfrid Sellar’s critique of Popper’s writing and Chapter 14 contains a fictional story between Socrates and Theaetetus to illustrate that even direct self-referencing sentences can hold meaning. Both these chapters are meant to provide additional support for Popper’s claims in Chapters 11 and 12.

The final segment of Conjectures and Refutations includes Chapters 15 to 20. They expand upon the uses and applications of critical rationalism to social organization and human nature. They also offer further insight into Popper’s political views. Chapter 15 discusses Hegel’s dialectic and criticizes it as a pseudo-scientific theory, since it cannot be falsified. Chapter 16 expands upon this idea by arguing that all attempts to predict the course of human history—a practice Popper dubs “historicism”—is based not on cutting-edge science but on dreams and myths. Chapter 17 reviews liberal principles and defends those that are conducive to critical evaluation and rational thinking. Chapter 18 is a condemnation of violence and tyranny, both of which Popper believes to be outdated and unconducive to scientific growth.

Finally, in Chapters 19 and 20, Popper reiterates his belief in human goodness, emphasizing his optimism for the future: At least in Western liberal societies, people’s intellectual curiosity and their desire to seek objective truth can be paired with a robust methodology of testing and falsification. These two elements are the fundamental building blocks of scientific growth.