postulates

postulate of causality the postulate that every phenomenon has a cause or causes; i.e., that events do not occur at random but in accordance with physical laws so that in principle causes can be found for each effect.

Koch's p's a statement of the kind of experimental evidence required to establish the causative relation of a given microorganism to a given disease. The conditions are: 1, the microorganism is present in every case of the disease; 2, it is to be cultivated in pure culture; 3, inoculation of such culture must produce the disease in susceptible animals; 4, it must be obtained from such animals, and again grown in a pure culture.