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How Not To Be a Chronological Snob (Post 15)

Historical “knowledge” was not the only casualty of the Enlightenment. Knowledge of moral and philosophical truth fared no better. I’ll outline how this led to our modern assumptions concerning what we can or cannot know about what is good, true, and beautiful.

Philosophy and Ethics: Now Opinions, Not Facts

The “Scientific Method”

Prior to the Enlightenment, truth was truth and facts were facts, regardless of the area of knowledge–science, history, philosophy, ethics, or theology. After the Enlightenment, many came to believe science was the only, or at least the best, way to know anything (scientism). Therefore, if any other field of study wanted a part of the action, it had to adapt to show that it too was “scientific.” Being “scientific” meant employing the “scientific method.” If this was not possible, knowledge could not be gained. Thus, the “scientific method” trumped all other methods for gaining knowledge.

Yet philosophy and ethics, as discussed in Post 13 of this series, require different methods and instruments, due to the nature of the subject matter. Therefore, given the assumptions of the Enlightenment, truths in philosophy could be no more than mere opinions, not facts

Cartesian Certainty

The writings of Enlightenment philosopher Rene Descartes made things even worse for ethics and philosophy. In Meditations on First Philosophy, he argued that we can base knowledge only on what is certain. And the only thing we can be certain of is that we are thinking. This is what he meant by the now-famous phrase, “I think, therefore I am” (cogito ergo sum).

Many accepted Descartes’s argument, from which developed the idea of “Cartesian certainty” (“Cartesian” is a way to refer to the ideas of Descartes). Cartesian certainty is the idea that if I can’t be 100% sure of something, I can’t know it or claim it is true. 

We often hear this assumption in conversations about belief in God. When I claim to know God exists, a non-believer will often ask me, “Can you prove that with 100% certainty? Is it possible that you might be wrong?” Of course, I can’t prove it 100%, and I might be wrong. To that, the non-believer responds, “Well, then, you can’t say you know God exists at all. It can’t be proven. It’s just blind faith.” This response is based on the assumption that knowledge requires 100% certainty–Cartesian certainty. I discuss this approach to knowledge and offer a critique here.

One consequence of Cartesian certainty becoming a paradigm of Enlightenment thinking was that claims made in fields such as philosophy and ethics, where 100% certainty cannot be attained, are mere beliefs rather than known facts. They are nothing more than personal and private opinions and values that people differ on, as people differ on what flavor of ice cream is best. Only in science can we have knowledge, because only in science we can “prove” things to be true. 

How We See This Idea Lived Out Today

In ethics, the result was relativism. Since we can’t know for sure what is right, morality became subjective and individual. What is right for you isn’t necessarily right for me, and vice versa. So no one should “impose” their morality on others. “To each his own” became the mantra. 

Its objective truthfulness undermined in this way, philosophical study was relegated to nothing more than a hobby for most. Sure, if someone has time to be “philosophical” for fun, that’s fine. But it was no longer seen as a noble, important, or even essential pursuit. Why should it be, if philosophical speculation is nothing more than whimsical musings that lead to nothing more than personal opinions, not knowledge about facts? 

Soon this perspective affected the educational curriculum. Prior to this shift, philosophy was an foundational element of education, all the way through a university education. It was an essential part of becoming adequately educated, in order to become virtuous people. Yet as this shift took root, students were required to study philosophy less and less (along with the other humanities). The emphasis was more and more on the sciences, where there was knowledge of facts, rather than endless discussions of opinions. (For more on the historical context, I will be releasing a podcast in the next week or so with historian Liam Atchison discussing these matters, available at

The Inconsistencies of the Modern Approach

We Can’t Give Up on Moral Absolutes

Those who desire to live out this Enlightenment shift in thinking find it exceedingly difficult to do so. Those arguing there is no ethical knowledge, but only opinion, should never make a moral judgment. However, they often do.

For instance, when a woman’s rights are violated, children of the Enlightenment still cry out for justice. Of course, they are right to do so. However, their cry is justified only if the Enlightenment assumption that moral values are mere opinions is actually false. Those embracing Enlightenment thinking can’t have it both ways! (I’ve said a bit more about this in my post When it Comes to Weinstein et al., No One is a Moral Relativist–And That’s a Good Thing! For another example, consider the current culture of shaming and silencing those with different views on moral issues concerning race and sexual identity.)

We Can’t Give Up on Philosophical Truths

Similarly, though children of the Enlightenment state that philosophical speculation is opinion, not facts that can be known, they don’t live as if this is true. Everyone has an idea on what we are, what the good life is and how it should be obtained, the nature of a family, whether a society should embrace socialism or capitalism, and so on. 

All these are philosophical ideas widely recognized as true (and therefore items of knowledge). Some children of the Enlightenment go so far as to write books to convince others their ideas on these topics are true. But this, again, is trying to have one’s cake and eat it too! 

The same point can be made concerning science itself, which rests on one’s philosophy of science. If there are no philosophical truths, there is no right philosophy of science, and therefore there is no justification for ideas such as the “scientific method.” (I’ve written more about this here.)

But wait, the inconsistency gets worse! Children of the Enlightenment are quick to allow some exceptions to this rule. Although philosophical speculation not using the “scientific method” is assumed unable to give us anything better than opinions, Descartes’s philosophical writings got special treatment. His philosophical ideas were taken to be true (as were the writings of some other Enlightenment philosophers such as Hume and Kant). So it turns out that, in practice, children of the Enlightenment really believe that those with “mere opinions” were the pre-Enlightenment philosophers who did not echo the popular ideas of the day–philosophers such as Plato, Aristotle, Augustine, and Aquinas. This seems to be a textbook case of the Special Pleading logical fallacy.

If Cartesian Certainty Is Required for Knowledge, Science Also Fails

A second inconsistency in this reasoning is that we can never prove scientific claims with 100% certainty either. Scientific “proof” simply means simply that the majority of evidence confirms one hypothesis over others. Yet it is always possible that in the future new evidence may overturn the theory that we currently consider “proven.” But this fact didn’t stop Enlightenment thinkers from saying science is about “facts” and philosophy and ethics is about “values” or “opinions.” (I’ve written more on this Fact/Value dichotomy in these posts.)


One key feature of truth is consistency. If a belief is true, it can be lived, day in and day out. On the other hand, if it is impossible to live out what one believes, then that belief is almost certainly false. The inconsistencies discussed in this post provide a good reason to conclude that reducing ethical and philosophical ideas from facts to values–and therefore from knowledge to opinion–is not the right way to go.

Next week I’ll look at similar issues related to the study of theology. 

Until then, grace and peace.

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