  By doing so, Cardano provides a definition of happiness which is inclusive of both knowledge and pleasure. Happiness consists in a “perception of pleasure” that is great (magna), full (plena), pure (pura), untroubled (secura), and safe (tuta) (De utilitate, OO, II, 37b; Theonoston, OO, II, 305b; De libris propriis, OO, I, 76b; ed. Maclean, 212–213). In Theonoston, happiness is said to coincide with a kind of inner composure understood not in terms of lack of sensibility (indolentia), but as a condition of mental vigour stemming from the contemplation of the true nature of things. If tranquillity consisted in mere refractoriness to unsettling experiences, the impassive state of a stone should then be viewed as the best condition (Theonoston, OO, II, 299b, 305b, 313b). By contrast, ethical peace rests on a state of cognitive tension and focus. In ways that remind us of the sea and the air, undisturbed calm (tranquilla quies) is always accompanied by a current of “light motion,” i.e., a state of balance between opposite conditions “which does not unsettle, but delights us.” Cardano’s tranquillitas is therefore not the same as absolute rest: “in its state of highest tranquillity, our soul is as it were tremulous and breathing” (Theonoston, OO, II, 300a, 305b). The incessant vitality of our being demonstrates that “the matter we are made of, being of a celestial origin, produced and entwined with motion, does not enjoy rest, but thrives on motion,” a motion that, in the final analysis, is no bodily activity, but an expression of knowledge and intellect (Theonoston, OO, II, 304a). True tranquillity results from a condition of inviolable self-fulfilment (securitas) based on resources that are in our power (in nostra potestate esse). Cardano is not convinced by the Senecan view of tranquillity as a balanced active life (vita actuosa), or by Socrates’s kind of ‘engaged’ tranquillity; in both cases, their behaviour is for Cardano symptomatic of ambition rather than being the indication of a truly committed philosophical life (Theonoston, OO, II, 306b). Finally, Cardano rejects the ideals of tranquillity championed by Plutarch, Antoninus and Cicero, viewed as models of ethical escapism devised by men who in their life never managed to reach a condition of stable serenity (Theonoston, OO, II, 305a).