Thomas Aquinas

“ Thus the life of plants is said to consist in nourishment and generation; the life of animals in sensation and movement; and the life of men in their understanding and acting according to reason. Wherefore also in men the life of every man would seem to be that wherein he delights most, and on which he is most intent ”

“ Now the intellect is divided into active and contemplative, since the end of intellective knowledge is either the knowledge itself of truth, which pertains to the contemplative intellect, or some external action, which pertains to the practical or active intellect. Therefore life too is adequately divided into active and contemplative. ”

“ All the occupations of human actions, if directed to the requirements of the present life in accord with right reason, belong to the active life which provides for the necessities of the present life by means of well-ordered activity. If, on the other hand, they minister to any concupiscence whatever, they belong to the life of pleasure, which is not comprised under the active life. Those human occupations that are directed to the consideration of truth belong to the contemplative life. ”