The mean can always be determined by reference to the two vices of excess and deficiency. All vices exceed or fall short of what is required by virtue in emotion and action, but virtue always finds and chooses the mean. By definition of its nature or essence, virtue is a mean, but in regard to general standards of what is right and good, virtue is an extreme.
We must note that it is impossible to choose a mean in regard to some actions or feelings. Emotions like malice and envy, actions like adultery, theft, and murder are evil in any form or degree. One can never do right by experiencing such feelings or committing such deeds. It is absurd to discuss whether there is a mean, excess, or deficiency in unjust, cowardly, or intemperate actions and emotions, for then one would end up with such ridiculous conceptions as a mean of excess, a mean of deficiency, an excess of excess, or a deficiency of deficiency. In the same way there can be no mean, excess, or deficiency in regard to such things as justice and temperance, for in a sense their mean is an extreme. Stated in general terms, there can be no mean in something which is an excess or deficiency, and there can be no excess or deficiency in a mean. Evil is evil in every form or degree; good is good in every form or degree.
