This chapter deals with the evolution of scientific epistemology following the impact of Kant’s critical philosophy, which emphasized the role of epistemology in learning and decision-making and sought to synthesize Empiricism and Rationalism. Kant’s ‘Copernican revolution’ shifted the focus of research towards the epistemic subject. This shift redefined the need for exploring the limits of knowledge and establishing the conditions for reliable scientific inquiry, while acknowledging the structuring role of the mind. Post-Kantian developments diverged in different cultural environments. German Idealism, notably Hegel, employed teleological dialectics to resolve the Kantian antinomies, viewing science as driven progressively towards a metaphysical ‘absolute’. The diverging paradigm of positivism, championed by Comte, emphasized the crucial role of empirical evidence in science. This paradigm focused on the capacity of prediction within the frame of a teleological view of progress. The nineteenth century saw also the rise of evolutionary thinking, first in biology (Darwin) and physics (thermodynamics). Mach aimed to integrate Darwinism and experimental psychology, influencing the genesis of the Vienna Circle. This circle fostered logical positivism, merging empiricism with formal logic, using the verifiability principle as a demarcation criterion between science and metaphysics. Internal tensions and intrinsic limitations led to its post-war decline paving the way for the emergence of post-positivism.

The first chapter traces the origins and evolution of the concept of rationality in Western thought, arguing that its root lies in the Greek concept of logos. It explores early philosophical attempts to grapple with the paradox of change originated by this concept of rationality, contrasting the views of Heraclitus and Pythagoras. A pivotal moment came from the Pythagorean discovery of irrational numbers, which shifted the foundations of rational arguments towards geometry. In particular, the chapter examines the Eleatic School’s denial of the reality of change as argued by Parmenides and Zeno and the atomists’ counter-arguments developed by Democritus and Epicurus. This chapter highlights the emergence of logical consistency as a core element of epistemic rationality. The role of dialectic in extending rationality to dialogue and evolution is analysed, distinguishing between the critical dialectic of Socrates and the teleological dialectic of Plato’s later works. Finally, the chapter introduces a crucial dichotomy between rationality viewed as progressive accumulation of true knowledge versus rationality as faculty of learning. This dichotomy sets the stage for the analysis of scientific pluralism developed in subsequent chapters. This chapter shows the importance of pluralism in fostering the rapid development of early Greek philosophy and science.