Version: v1, Published online: 1998
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2. The parts of philosophy
The Stoics formally sanctioned what was to become thereafter the canonical division of philosophy into three parts: physics, logic and ethics. Stoicism is arguably the first fully and self-consciously systematic philosophy. In the next three paragraphs correspondences will be noted between these three main areas of philosophy and the individual topics covered in the following sections. However, some of these topics (especially those in §§6–9, 14, 20) may not fit quite as neatly into any one of the three areas as the schematization implies.
Logic (§§10–13), the science of rationality (derived from logos, ‘reason’), included not only inferential logic in the modern sense (more correctly called ‘dialectic’ by the Stoics), but also theory of knowledge, in which generation after generation of Stoics defended the existence of cognitive certainty against sceptical attacks. All Stoics, with the exception of Ariston of Chios, regarded logic as a fundamental part of philosophy.
Physics (§§3–9) – the study of nature (physis) – was a largely speculative or theoretical discipline, concerned with understanding the world’s rational structure, and therefore embracing such diverse disciplines as biology, psychology and theology within its scope. It drew on the findings of contemporary scientists, but was not itself any kind of empirical science. Indeed, opponents accused it of wilful blindness to inconvenient new scientific discoveries, such as the demonstration by Alexandrian doctors that the rational mind is in the head, not the chest. Physics presupposed logic, at least to the extent that its findings were largely developed in strings of syllogisms.
Ethics (§§14–19), the authentically Socratic core of Stoic philosophy, was the discipline which described how happiness could be achieved. It presupposed physics, which supplied an understanding of the world’s rational structure and goodness and of the individual’s place in it.
There was less agreement about how the three parts related to each other. One favoured model compared philosophy to an orchard in which logic was the protective outer wall, physics the soil and trees, and ethics the fruit. Posidonius favoured the analogy to a living animal, in which logic was the bones and sinews, physics the flesh and ethics the soul. These and other analogies probably agreed in making ethics the ultimate aim and crowning achievement of philosophy. The value of physics and logic was in a way instrumental – to acquire the understanding which would make a happy life possible. But that understanding, a perfected rationality, was itself so integral to the Stoic conception of happiness that to call it instrumental may be to underestimate the true unity of Stoic philosophy.
Most leading Stoics put the three parts of philosophy into the sequence logic–physics–ethics, but some favoured other orders. Here they are likely to have been specifying nothing more than the best order in which to teach it, with no implications which might threaten its conceptual unity.
Sedley, David. The parts of philosophy. Stoicism, 1998, doi:10.4324/9780415249126-A112-1. Routledge Encyclopedia of Philosophy, Taylor and Francis, https://www.rep.routledge.com/articles/thematic/stoicism/v-1/sections/the-parts-of-philosophy.
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