In the pre-modern natural philosophical scheme all animate and inanimate things located in the elemental spheres of the world were conceived as composites of the ‘pure and unadulterated’ qualities of heat, coldness, dryness and moisture. It followed that each of the four humours (the bodily fluids present in man which were named in the English tradition as blood, phlegm, choler and melancholy) were mixtures of the absolute elements, and were sensitive to environmental and cosmological changes. Theoretically, an optimally functioning body required appropriate levels of each of the different humours. However, the ideal seemed impossible to achieve in practice. The overall bodily ratio of warmth and cold, moisture and dryness supposedly varied naturally through the seasons and in accordance with a person's age, sex and physical surroundings. Minor variations were considered normal, but if the disproportion was great, or if the humours putrefied because of some external factor acting upon them, then disease (it was believed) would invariably result.

A person might rebalance or strengthen their constitution by ingesting a substance in which the missing qualities predominated, be it in the form of a food, a plant product, a compound drug (customized to suit the individual patient) or a vapour. The restorative power of food, for example, was recognized in the private correspondence of Norfolk's most famous gentry family, the Pastons, who (amongst other properties and estates) had a town house in Coslany in the west of Norwich. In late September 1443, Margaret Paston dictated this earnest message in a postscript to a letter to her husband, who had recently suffered a ‘grete dysese’: