One argument that rationalists have used to argue that not all knowledge is derived from experience is that some of our knowledge is innate. Innateness is a hard concept to pin down but innate knowledge can be thought of as knowledge that is unlearned. One way of understanding the debate between rationalism and empiricism is that rationalists have argued that experience cannot adequately explain all of our knowledge and so we need to appeal to innate knowledge whereas empiricists have claimed on the contrary that all of our knowledge can be derived from experience and so we don't need innateness as a source of knowledge. This is not a perfect way of dividing rationalists and empiricists but, historically, the denial of innate ideas has been an important part of empiricism and has even been proposed as a defining part of empiricism. Whether or not empiricism can be defined so simply, innateness is an interesting source of knowledge that has remained an important issue for debate throughout the history of philosophy up to the present day.


An animation of the geometry problem that Socrates walks the slave through.

In the Meno, Plato argues for innate knowledge via a dialogue between Socrates and a slave who has had no training in mathematics. Through a series of questions, Aristotle prompts the slave to go through the following reasoning:

  • The square at the bottom left is 1x1 so it has an area of 1
  • The question is: what square will have double the area (i.e. area = 2)?
  • It isn’t a 2x2 square because we see the area of the big 2x2 square is made up of four little squares (so the area is quadrupled)
  • But if we cut these little squares in half then the areas of each of them is halved.
  • Doing this forms a rotated square; adding up the four halves we find that its area is ½ + ½ + ½ + ½ = 2
  • So this is the square with double the area!

Plato argues that because the slave has not been educated in mathematics and because he is led to discovering the answer for himself rather than being given the answer, they must be remembering knowledge that is given to them innately. Opponents of this argument note that the questions Aristotle asks in the dialogue can be read as leading questions and it seems that he may simply be providing the slave with the answer through cleverly framed questions.

In the Phaedo, Plato uses the example of equality to argue that our abstract ideas must be innate. Once again Socrates is portrayed in dialogue, this time questioning a man who believes that we can gain our idea of equality through experience of things such as equal pieces of sticks. Socrates argues that nothing we ever experience is perfectly equal and so falls short of our idea of perfect equality. But if our idea of perfect equality cannot be found in our experience, then it must come from somewhere else, specifically it must be innate. This applies to all of our ideas which are too general and abstract to be found anywhere in our experience and so seems to indicate that we must have many innate ideas. Whilst Plato here is arguing for innate ideas rather than innate knowledge, it is still important in a discussion of innateness as a source of knowledge because (as Locke argued) it is plausible that for us to know a proposition we must have all the ideas contained in the proposition. For example, to have innate knowledge that "there is a God" requires that we have an innate idea of God that gives the proposition meaning.


The first book of Locke's An Essay Concerning Human Understanding is dedicated to arguing that there are no innate ideas or knowledge. Locke's broad argument throughout book I is that if there was any knowledge that was innate, then everybody should agree to it but according to Locke there are no propositions that all people agree to because infants, "idiots", and those that haven't considered the propositions do not agree to them. This means that none of the knowledge we have could possibly be innate. Furthermore, innate knowledge requires that we have innate ideas of the things we know about but we do not have any innate ideas because infants do not have these ideas (e.g. ideas of God, equality, impossibility not in infants). Locke considers many possible counterarguments that could be used to counter his point.

  • We have innate knowledge but it is uncovered by reason. Locke argues that if the knowledge is uncovered by reason then it cannot possibly be innate because reasoning is the process of inferring what is unknown from what is known. Furthermore, if innate knowledge is uncovered by reason then would this not mean that almost all of our knowledge including knowledge that does not seem innate at all but rather seems learned including all mathematical theorems would be innate. This seems to make the innatists claim trivial, if their definition of innateness is this broad then all of our knowledge (including learned and derived knowledge) counts as innate. Locke continues to argue that it is not even true that children agree to the knowledge that is thought of as innate when they come to reason because the knowledge that is thought of as innate is far too abstract for children to consider at the age they come to reason and even many adults may not think of it. This is because knowledge that is often thought of as innate is abstract and logical truths such as "it is impossible for the same thing to be and to not be".
  • We have innate knowledge but it is only agreed to when proposed and understood. Once again Locke argues that this makes innateness too broad because even quite trivial propositions such as "bitter is not sweet" are agreed to when proposed and understood. He also questions whether knowledge that is only agreed to when proposed to someone could possibly be innate by asking the rhetorical question "doth the proposing them print them clearer in the mind than nature did?"
  • We have innate knowledge but it is only known implicitly. Locke argues that if knowledge is innately imprinted onto the mind that it cannot be implicitly known because according to Locke "No proposition can be said to be in the mind which it never yet knew, which it was never yet conscious of". Locke goes on to argue that implicitly known propositions are incoherent saying "that a truth should be innate and yet not assented to, is to me as unintelligible as for a man to know a truth and be ignorant of it at the same time". These arguments rest on an assumption that all areas of the mind are open to conscious access. As we will see, this is a point that Leibniz utilises in his defense of innate ideas.

Locke hopes to strengthen his case against innate knowledge by showing that all of our knowledge can be derived from experience with the use of his empiricist theory. According to Locke, we are born a "tabula rasa" or blank slate without any knowledge or ideas. Through perception we are furnished with all of our ideas and our knowledge. These ideas can be broken down into simple ideas which are the basic building blocks of all of our ideas and which themselves cannot be broken down. These ideas can be combined in many different ways to create all kinds of complex ideas. For example, our idea of a horse may be built from ideas such as the horse having a certain shape, colour, movement and sound (e.g. HORSE = HORSE-SHAPED + BROWN + GALLOPING + NEIGHING). The ideas that we have can be compared with one another to see how similar or dissimilar they are from one another. We can come to our abstract ideas such as equality by a process of abstraction in which we compare our ideas and remove all the differences between them until we get to an idea that only has the similarities between all of our ideas that have equality. Likewise, we can come to a general abstract idea of "human" by comparing all our ideas of particular people and taking away all the differences between people until we get an abstract idea that applies to everyone.


In his New Essays Concerning Human Understanding, Leibniz puts forward a similar argument to Plato's argument about equality. Leibniz argues that experience cannot provide us with knowledge of necessary truths because we only ever experience particular instances but we cannot derive any necessary truths from particular instances because it does not follow that just because something has happened that it must keep on happening. Leibniz then says that the only way that we could possibly know these necessary truths (if not by experience) is that they are just innate. As Leibniz puts it:

Although the senses are necessary for all our actual knowledge, they are not sufficient to provide it all, since they never give us anything but instances, that is particular or singular truths. But however many instances confirm a general truth, they do not suffice to establish its universal necessity; for it does not follow that what has happened will always happen in the same way. Necessary truths, such as we find in pure mathematics and particularly in arithmetic and geometry, must have principles whose proof does not depend on instances nor, consequently, on the testimony of the senses [...] and so the proof of them can only come from inner principles, which are described as innate.

Leibniz also responds to Locke's arguments against innate knowledge by utilising a conception of the unconscious as well as arguing that some of our innate knowledge comes in the form of tendencies in our way to think and reason rather than in propositions. For example, in response to Locke's suggestion that our mind begins a blank slate without any ideas or knowledge imprinted onto it, Leibniz writes the following passage:

I have also used the analogy of a veined block of marble, as opposed to an entirely homogenous block of marble, or to a blank slate – what the philosophers call a tabula rasa. For if the soul were like such a blank tablet then truths would be in us as the shape of Hercules is in a piece of marble when the marble is entirely neutral as to whether it assumes this shape or some other. However, if there were veins in the block which marked out the shape of Hercules rather than other shapes, then that block would be more determined to that shape and Hercules would be innate in it, in a way, even though labour would be required to expose the veins and to polish them into clarity, removing everything that prevents their being seen. This is how ideas and truths are innate in us – as inclinations, dispositions, tendencies, or natural potentialities

Contemporary debates about innatenessEdit

[Chomsky, maybe Fodor, moral innatism, innatism in other areas]