Principle (chemistry)

In modern chemistry, principles are the constituents of a substance, specifically those that produce a certain quality or effect in the substance, such as a bitter principle, which is any one of the numerous compounds having a bitter taste.

In pre-modern chemistry and alchemy, principles were the five fundamental substances believed to constitute all bodies. Three of these were called active or hypostatical principles: salt; sulfur, or oil; and spirit, or mercury. The salt was supposed to be the foundation of all savors; the sulfur, of odors; and the spirit, or mercury, of colors. The two passive or elementary principles were phlegm (or water), and earth (or caput mortuum).