Are all human beings equal? – Of course, that’s why we call them human. – But how do we know? – Well, it’s not a matter of empirical discovery, it’s our premise. – I see. And so everything else follows?
The opposition between empiricism and rationalism is often introduced as an epistemological dispute, concerning primarily the ways knowledge is acquired, warranted and limited. This is what I learned as a student and what is still taught today. If you’ve studied philosophy for a bit, you will also have heard that this opposition is problematic and coarse-grained when taken as a historical category. But in my view the problem is not that this opposition is too coarse-grained (all categories of that kind are). Rather, the problem lies with introducing it as a mere epistemological dispute. As I see it,* the opposition casts a much wider conceptual net and is rooted in metaphysical and even political ideas. Thus, the opposition is to be seen in relation to a set of disagreements in both theoretical and practical philosophy. In what follows, I don’t want to present a historical or conceptual account, but merely suggest means of recognising this wide-ranging set of ideas and show how the distinction helps us seeing the metaphysical implications and political choices related to our epistemological leanings.
Let me begin with a simple question: Do you think there is, ultimately, only one true description of the world? If your answer is ‘yes’, I’d be inclined to think that you are likely to have rationalist commitments. Why? Well, because an empiricist would likely reject that assumption for the reason that we might not be able to assess whether we lack important knowledge. Thus, we might miss out on crucial insights required to answer that question in the first place. This epistemological caution bears on metaphysical questions: Might the world be a highly contingent place, subject to sudden or constant change? If this is affirmed, it might not make sense to say that there is one true description of the world. How does this play out in political or moral terms? Rephrasing the disagreement a bit, we might say that rationalists are committed to the idea that the world is ordered in a certain way, while empiricists will remain open as to whether such an order is available to us at all. Once we see explanatory order in relation to world order, it becomes clear that certain commitments might follow for what we are and, thus, for what is good for us. If you believe that we can attain the one true description of the world, you might also entertain the idea that this standard should inform our sciences and our conduct at large. – Of course, this is quite a caricature of what I have in mind. All I want to suggest is that it might be rewarding to look whether certain epistemological leanings go hand in hand with metaphysical and practical commitments. So let’s zoom in on the different levels in a bit more detail.
(1) Epistemology: As I have already noted, the opposition is commonly introduced as concerning the origin, justification and limits of knowledge. Are certain ideas or principles innate or acquired through the senses? Where do we have to look in order to justify our assumptions? Can we know everything there is to be known, at least in principle, or are there realms that we cannot even sensibly hope to enter? – If we focus on the question of origin, we can already see how the opposition between empiricism and rationalism affects the pervasive nature-nurture debates: Are certain concepts and the related abilities owing to learning within a certain (social) environment or are the crucial elements given to us from the get-go? Now, let’s assume you’re a rationalist and think that our conceptual activity is mostly determined from the outset. Doesn’t it follow from this that you also assume that we are equal in our conceptual capacities? And doesn’t it also follow that rules of reasoning and standards of rationality are the same for all (rather than owing, say, to cultural contexts)? – While the answers are never straightforward, I would assume at least certain leanings into one direction or another. But while such leanings might already inform political choices, it is equally important to see how they relate to other areas of philosophy.
(2) Metaphysics: If you are an empiricist and assume that the main sources of our knowledge are our (limited) senses, this often goes and in hand with epistemic humility and the idea that we cannot explain everything. Pressed why you think so, you might find yourself inclined to say that the limits of our knowledge have a metaphysical footing. After all, if we cannot say whether an event is fully explicable, might this not be due to the fact that the world is contingent? Couldn’t everything have been otherwise, for instance because God interferes in events here and there? In other words, if you don’t assume there to be a sufficient reason for everything, this might be because you accept brute facts. Accordingly, the world is a chancy place and what our sciences track might be good enough to get by, but never provide the certainty that is promised by our understanding of natural laws. Depending on the historical period, such assumptions often go hand in hand with more or less explicit forms of essentialism. The lawful necessities in nature might be taken to relate to the way things are. Now essences are not only taken to determine what things are, but also how they ought to be. – Once you enter the territory of essentialism, then, it is only a small step to leanings regarding norms of being (together), of rationality, and of goodness.
(3) Theology / Sources of Normativity: If you allow for an essentialist determination of how things are and ought to be, this immediately raises the question of the sources of such essences and norms. Traditionally, we often find this question addressed in the opposition between theological intellectualism (or rationalism) and voluntarism: Intellectualists assume that norms of being and acting are prior to what God wills. So even God is bound by an order prior to his will. God acts out of reasons that are at least partly determined by the way natural things and processes are set up. By contrast, voluntarists assume that something is rational or right because God wills it, not vice versa. It is clear how this opposition rhymes with that of rationalism and empiricism: The rationalist assumes one order that even binds God. The empiricist remains epistemically humble, because she believes that rationality is fallible. Perhaps she believes this because she assumes that the world is a chancy place, which in turn might be owing to the idea that the omnipotent God can intervene anytime. It is equally clear how this opposition might translate into (lacking) justifications of moral norms or political power. – Unlike often assumed in the wake of Blumenberg and others, this doesn’t mean that voluntarism or empiricism straightforwardly translate into political absolutism. It is hardly ever a particular political idea that is endorsed as a result of empiricist or rationalist leanings. Nevertheless, we will likely find elements that play out in the justification of different systems.**
Summing up, we can see that certain ideas in epistemology go hand in hand with certain metaphysical as well as moral and political assumptions. The point is not to argue for systematically interwoven sets of doctrines, but to show that the opposition of empiricism and rationalism is so much more than just a disagreement about whether our minds are “blank slates”. Our piecemeal approach to philosophical domains might have its upsides, but it blurs our vision when it comes to the tight connections between theoretical and practical questions which clearly were more obvious to our historical predecessors. Seen this way, you might try and see whether you’ll find pertinently coherent assumptions in historical or current authors or in yourself. I’m not saying you’re inconsistent if you diverge from a certain set of assumptions. But it might be worth asking if and why you conform or diverge.
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* A number of ideas alluded to here would never have seen the light of day without numerous conversations with Laura Georgescu.
** See my posts on Ockham’s and Wittgenstein’s voluntarism for more details.
Handling Ideas 
I think what you say here is correct on the whole. I arrived at a similar conclusion, but by probably less reliable means. I study Kant, and something like this picture of multi-facetedness explains why Kant’s attacks on his predecessors were so multi-faceted. Empiricism and rationalism alike, by Kant’s lights, suffered one great error, which Kant called “transcendental realism.” The more I worked to understand what Kant thought transcendental realism amounted to, the more I saw that Kant thought of it as woven out of metaphysical, epistemological, theological, political, and moral threads, and I took that to mean he thought rationalism and empiricism were so woven. And, assuming Kant was on to something, I revisited some paradigmatic works from the so-called empiricist and rationalist traditions. I can certainly see what he meant.
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I really like this sort of integrative question. But the empiricist vs. rationalist distinction is, I think, too blunt to cut into the matter that helps to decide political sympathies. Look at end results: Hobbes and Locke both empiricist, but very different politically; Descartes and Spinoza both rationalist, but also politically very different. But maybe methodology – and more particularly, questions of trust, as well as questions of motivation and intent – lead to both epistemological and political differences. Hobbes and Spinoza were distrustful and sought “safe spaces” to do their own work; Descartes and Locke trusted local authorities and sought to initiate systematic programs; so on.
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