Leibniz in his response to Locke, argued that Locke had misunderstood what innate knowledge is. Locke had defined innate knowledge as true propositions universally known. Since infants and people with mental disabilities lacked these propositions, Locke argued, they were not universal, and therefore, could not be innate.
Leibniz argued that innate knowledge was a congenital propensity to acquire certain propositions, not the propositions themselves. Certain occurrences in life would normally “trigger” the propensity, and so we would acquire the propositions. Infants, so far as one could tell, simply had not been “triggered” yet.
Since propositions are made up of concepts, one could use the same argument concerning innate concepts. Our minds are predisposed to form certain concepts, provided they are exposed to the right stimuli. Leibniz used the analogy of a block of marble to convey this argument. Just as artists say the form of the statue is already within the marble, because of the structure of its veins, so the concepts are already within our minds. The chisel unlocks the statue from the block, and experience unlocks the concepts within our minds.
Science has moved on since the Enlightenment. Now many scientists argue that there are innate concepts and propositions, genetically-encoded in us and animals. Birds are instinctually able to complete the songs of their species, despite only hearing phrases of those songs from their parents. Human babies appear, at around five months old, to grasp the concept of mind independent objects.
This research only pushes the problem a step back, however. The concepts may be innate now, but if they were acquired through evolutionary processes, then the question still remains concerning their ultimate origin. A materialist who concedes the existence of innate knowledge might argue that it is the product of random mutation and natural selection. A theist would argue that God is the ultimate source of our knowledge and concepts: that proposition is more important to the Christian than the means by which God put the knowledge into us.
Ultimately, this epistemological problem must fit into a larger debate. It fits within bigger arguments concerning objective truth, the nature of knowledge, dealing with uncertainty, and knowing that God exists. Without objectivity, all our endeavours slip back into chaos and oblivion. Meaning presupposes objectivity.
Our concepts and knowledge must ultimately lead back to God. Quine argued that we are ontologically committed to the concept of God: we cannot reason without presupposing that God exists. This places us in a curious position as philosophers. Long before Quine, Kant was concerned with the ontological argument advanced by St Anselm (which subsequently faced challenges by Gaunilo and has also met attempts to rehabilitate or restate it).
Kant was concerned with the nature of the proposition, “God exists.” Analytic propositions, argued Kant, tell us only about the structure of our thoughts, not about how the world itself is. If the proposition, “God exists”, is analytic, it tells us only that our thinking presupposes the existence of God, not that there is actually a God “out there”.
Kant argued that propositions about the existence of things are synthetic; they are really claims that something in the world of experience corresponds to a concept in our minds. Propositions about existence, however, can only be known a posteriori – from experience. But how could one understand our everyday experience to confirm the existence of God? Such claims of experience would always be open to the challenge that they were subjective.
Thus, returning to Quine, if we are compelled to believe in God, but that belief does not connect with Something objective, we find ourselves in a curious paradox. The question, then, is really about perception. If we are connected to God through perception, then we know that He exists. This a posteriori route is not an exclusive way to God. The origin of our concepts and knowledge, discussed above, is also potentially an a priori route to God. If both routes have been provided, so that all men potentially may be saved, then St Paul is correct in stating that all men are without excuse regarding knowledge of God’s existence: God, in His grace, has provided ways for everyone.