A scientific theory is a good theory if it satisfies two requirements: It must accurately describe a large class of observations in terms of a model that is simple enough to contain only a few elements, and it must make definite predictions about the results of future observations  For example, Aristotle' s cosmological theory, which claimed that everything was made out of four elements -- earth, air, fire, and water -- satisfied the first requirement, but it did not make any definite predictions
Thus, Aristotle' s cosmological theory was not a good theory
Aristotle's cosmological theory described a large class of observations in terms of only four elements.