A man cannot acquire science by nature, or without teaching: but he may acquire Intellect and Sagacity by nature, simply through, long life and abundant experience.

The affirmations and opinions of old men deserve attention, hardly less than demonstrations: they have acquired an eye from experience, and can thus see the practical principles (though they may not be able to lay out their reasons logically) (XI.).
But an objector may ask--Of what use are Philosophy and Prudence?
He may take such grounds as these.

(1) Philosophy has no practical aim at all; nor does it consider the means of happiness?
(2) Prudence, though bearing on practice, is merely knowledge, and does not ensure right action.

(3) Even granting the knowledge to be of value as direction, it might be obtained, like medical knowledge, from a professional adviser.
(4) If philosophy is better than prudence, why does prudence control philosophy?
We have to answer these doubts.

The first is answered by asserting the independent value of philosophy and prudence, as perfections of our nature, and as sources of happiness in themselves.
The second and third doubts are set at rest, by affirming prudence to have no existence apart from virtue.