'Tis a sign of crudity and indigestion to disgorge what we eat in the same condition it was swallowed; the stomach has not performed its office unless it have altered the form and condition of what was committed to it to concoct.

Our minds work only upon trust, when bound and compelled to follow the appetite of another's fancy, enslaved and captivated under the authority of another's instruction; we have been so subjected to the trammel, that we have no free, nor natural pace of our own; our own vigour and liberty are extinct and gone: "Nunquam tutelae suae fiunt." ["They are ever in wardship."-- Seneca, Ep., 33.] I was privately carried at Pisa to see a very honest man, but so great an Aristotelian, that his most usual thesis was: "That the touchstone and square of all solid imagination, and of all truth, was an absolute conformity to Aristotle's doctrine; and that all besides was nothing but inanity and chimera; for that he had seen all, and said all." A position, that for having been a little too injuriously and broadly interpreted, brought him once and long kept him in great danger of the Inquisition at Rome.
Let him make him examine and thoroughly sift everything he reads, and lodge nothing in his fancy upon simple authority and upon trust.
Aristotle's principles will then be no more principles to him, than those of Epicurus and the Stoics: let this diversity of opinions be propounded to, and laid before him; he will himself choose, if he be able; if not, he will remain in doubt.
"Che non men the saver, dubbiar m' aggrata." ["I love to doubt, as well as to know."-- Dante, Inferno, xi.

93] for, if he embrace the opinions of Xenophon and Plato, by his own reason, they will no more be theirs, but become his own.

Who follows another, follows nothing, finds nothing, nay, is inquisitive after nothing.
"Non sumus sub rege; sibi quisque se vindicet." ["We are under no king; let each vindicate himself." -- Seneca, Ep.,33] Let him, at least, know that he knows.

It will be necessary that he imbibe their knowledge, not that he be corrupted with their precepts; and no matter if he forget where he had his learning, provided he know how to apply it to his own use.