"On the manner of fasting a uniform rule cannot easily be observed, because everybody has not the same strength; nor is it like the rest of the virtues, acquired by steadfastness of mind alone. And therefore, because it does not depend only on mental firmness, since it has to do with the possibilities of the body, we have received this explanation concerning it which has been handed down to us, viz.: that there is a difference of time, manner, and quality of the refreshment in proportion to the difference of condition of the body, the age, and sex: but that there is one and the same rule of restraint to everybody as regards continence of mind, and the virtue of the spirit."