Pneuma is the central concept of Stoic physics: a subtle "fiery breath," a mixture of fire and air, pervading the whole cosmos and binding it into a single whole (συμπάθεια). In the human being the Stoics distinguish several grades of pneuma: φυτική (vegetative — growth), ζωτική (animal — vital force), αἰσθητική (perceptive), and λογιστική (rational), with the highest layer identical with the TERMruling part and the TERMintellect. In the narrow, bodily sense, pneuma is simply breath — ephemeral and constantly exchanged.

SVF I 134–144 (Zeno's doctrine of the pneuma); II 439–462 (Chrysippus on the four grades of pneuma); II 773–800 (pneuma as "the body of the soul"); DL VII 156–157; LS 47, 53. In Marcus: Med. 2.2; 4.41; 6.15; 9.2; 12.30.

In 02-02 Marcus uses precisely the diminutive πνευμάτιον ("little breath") and immediately reduces it to bare physics: "a breath that does not stay self-identical, exhaled and inhaled again hour by hour." This is not a denial of the Stoic doctrine of higher pneuma as rational — it is the inverse, ascetic move: so long as attention dwells on breath as a biological process, breath is stripped down to mere matter; the "I" proper is the TERMruling part, the third and only significant component. See unity-of-cosmos (pneuma as cosmic bond) and definitio (the exercise of the "stripped-down view").