_ Source: _Volume 61, Issue 1, pp 82 - 109 Galen talks about tension, _tonos_, in a physiological sense, which seems to be related to either the innate heat of the living being, the good mixture of its humors, or the body’s _pneuma_. This paper shows that Galen, with some important distinctions concerning the substance of the soul, derives this use of _tonos_ from the Stoics. But beyond that, it shows that Galen uses _tonos_ in a strict psychological sense derived (...) from Plato as well, and integrates it in his characterization of the operations of the spirited part of the soul. (shrink)