But virtue is, in reality, a qualification of the mind, although the term equivalent to virtue in every language, implies all the required effects and appearances of this qualification.
Its constituents are, Disposition, Skill, Application, and Force.
Corresponding to the number of these constituents, virtue has been divided into four capital branches, called the Cardinal Virtues.
These are, Justice, Prudence, Temperance, and Fortitude.
Justice, is the regard shown to the rights and happiness of mankind.
Those effects of justice which mere innocence implies, are required under the sanction of compulsory law.
Those that constitute beneficence, are required under the sanctions of duty only.
Prudence is that discernment by which men distinguish the value of ends, and the fitness of means to obtain them.
Without this qualification, men are not fitted to act with any measure of steadiness consistency, or good effect.
Temperance is abstinence from inferior pleasures or amusements that mislead our pursuits.
No one can apply himself effectually to any worthy purpose, who is liable to the interruption of mean pleasures or amusements, that occupy an improper part of his time, that stifle his affections, or impair his faculties.
The maxim of temperance is, that a person, having once ascertained what his best and happiest engagements are, ought to count every moment lost, that, without necessity, is otherwise employed.
Fortitude is the power to withstand opposition, difficulty, and danger.
All the good qualities of men have a reference to some effect that is to be produced, and have a merit proportioned to some difficulty that is overcome. Hence dispositions and capacities of any sort are of no avail, without resolution, and force of mind.
*This division is so natural, that it has always presented itself when we have treated of the felicity or excellence competent to man's nature.
Adam Ferguson, Institutes of Moral Philosophy: A New Edition, Enlarged, VI.5.1 (p. 182). The disposition-skill-application-force explanation is interesting but not, as far as I can see, adequately explained anywhere. That we start with the disposition, which is refined by skill, which is then applied, which may be done with force, makes sense, but the connection of, say, Temperance with application seems a bit strained. In any case as Aquinas noted, there are several different readings of the list of cardinal virtues; Ferguson's is a general-properties-of-virtue reading.