In the First Part of the Summa theologiae, Thomas Aquinas cites Aristotle to the effect that the intellect is like “a tablet on which nothing is written."  That’s in the sed contra, his restatement of the traditional view.  But then in his own response, he agrees:  Man's potential knowledge is transformed into actual knowledge "through the action of sensible objects on his senses," so that the soul "has no innate species" (no innate knowledge of forms).

WHAT?  My whole academic life, I have been hearing that Locke rejected the innate ideas in which his predecessors supposedly believed, calling our minds a tabula rasa or blank slate.  I must be missing something, because surely those critics had read this passage in Aquinas.  Would you be so kind as to enlighten me as to why Locke is so different from Aquinas here?



Yes, I had the same reaction when I was first studying Aristotle and Thomas Aquinas!  However, the notion of innate knowledge does not come from those two luminaries – I don’t know why people say this.  And really, the notion is crazy.  If there were such a thing as innate knowledge, then even the baby freshly popped from the womb would have it.  Fancy a newborn thinking to himself, “I must never do anyone undue harm -- whatever doing is, whatever harm is, and whatever it is to be undue”!

St. Thomas certainly believes in natural knowledge.  He says so in the very section you quote.  Of course he doesn’t think all our knowledge is natural, or else we would never forget anything, and even a blind person would know what color is.  Now here’s the kicker.  According to him, not even natural knowledge is innate.  Even natural knowledge depends, in a way, on sense experience.  Someone who had never had sense experience wouldn’t know anything.

Let’s think about this.  There are certain things that a person who has reached the age of reason naturally knows, but he isn’t born with this knowledge.  For example, an infant doesn’t innately know that two things equal to a third thing are equal to each other.  But when the proposition is taught to a twelve-year-old who understands the meanings of such terms as “equal,” he can’t help but see that it is true.  The knowledge is per se nota, “known in itself.”

Does he know it just because someone has taught it to him?  No.  Your mother and father taught you the Golden Rule, but you didn’t believe it just because they said it was true; you believed them because when they said it, you could see for yourself that it was true.  What they did by their teaching was call your attention to this truth, and what they said made sense to you.

Even per se nota knowledge depends on sensory experience, because if you had never perceived any things which were equal, you wouldn’t understand what equality is, and so you wouldn’t grasp that two things equal to a third thing are equal to each other.  Yet in another sense such knowledge transcends sensory experience, because even though you haven’t seen all equal things, you know that the proposition “two things equal to a third thing are equal to each other” must be true – even of the equal things you haven’t seen!

According to St. Thomas, the reason your mind can know such a thing is that the universal forms of things are implicit in sense experience, and the rational mind extracts them.  A bird, which is not rational, knows only particulars:  This worm, this branch, this nest.  In fact, since it doesn’t possess the concepts of worm as such, branch as such, or nest as such, even that way of putting it falsifies the bird’s knowledge.  All it really knows is this, this, this!  By contrast, when you see a worm, you recognize it as an individual instance of worm.  This is stupendous.

Our power to grasp universal forms is what makes it possible for us to formulate predications:  To say, for example, that man is a rational animal, or that undue harm must not be done.  When a proposition is per se nota, the mind recognizes that the predication expressing it has to be true, just from the meanings of the terms it employs.  The subject, man, contains the meaning of the predicate, rational animal, so of course “man is a rational animal” is true.  The subject, undue harm, contains the meaning of the predicate, something that must not be done, so of course “undue harm must not be done” is true.  By contrast, the proposition “the table is made of brass” is not per se nota, because the subject, table, does not contain the meaning of the predicate, made of brass.  The table might be made of wood, plastic, dark matter, pixie dust, or something else.

Now Locke doesn’t differ from Aristotle and Thomas Aquinas merely because he believes that the mind learns from experience.  Locke differs from them because he and the other empiricists radicalize the idea, trying to make sense of it without recourse to real forms or essences.

Aristotle and St. Thomas would have considered that impossible.  And I think it is. 

You might think of it this way.  The mind of a bird is a blank slate, and the mind of a human being is also a blank slate.  But what can be written on the bird and the human being slates differs radically, and so does the way it is written there.  The mind of a bird takes in only the particulars of a thing; the mind of a rational being takes in its form or essence.

And just for that reason, the slate is not blank in the peculiar sense that some people give to the expression tabula rasa, for not just anything can be written on it – and some things can’t help but be written on it.  There are some things that a rational being of the age of reason can’t not know, and cannot disbelieve even if he tries.


Commentary on Thomas Aquinas's Treatise on Law

What We Can't Not Know: A Guide