Leading analytic philosophers, like Timothy Williamson and Derek Parfit, argue that common sense is a way of testing the truth of philosophical theories. If philosophy seems to contradict what we take to be commonsense knowledge, they argue, so much the worse for philosophy. But common sense can be wildly misleading, merely reflecting the prejudices of a particular culture or era. What was once considered common sense knowledge is today known to be false. Instead of relying on common sense, philosophy should consider using scientific knowledge as a starting point and test for its claims, argues Marcus Arvan.

In Doing Philosophy: From Common Curiosity to Logical Reasoning, Timothy Williamson contends that philosophy starts from commonsense, and that commonsense can serve as a ‘check on the philosopher’s provisional conclusions’. As an example of the latter, Williamson contends that our commonsense knowledge that people often eat breakfast after getting up in the morning refutes philosophical arguments that time is unreal. Williamson is far from alone in thinking along these lines.

It is commonplace in philosophy to test arguments and theories by reference to commonsense. For example, Derek Parfit argues influentially against the subjectivity of value by inviting us to imagine someone who wants to experience future agony. Parfit notes that if subjectivism were true, then such a person would have decisive reasons to pursue agony. But, Parfit says, ‘[t]hat is hard to believe’, which he offers as evidence that subjectivism is false. Another common philosophical methodology, reflective equilibrium, holds that the role of philosophy is to make commonsense judgements about principles and concrete cases more coherent, thus grounding philosophical theory in what most people already believe.

But there are good reasons to doubt whether commonsense should play these roles in philosophy.

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Appeals to common sense in philosophy are a demonstrably unreliable method for distinguishing genuine knowledge (and truth) from mere belief (and falsehood).

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Philosophy vs Common Sense

First, as Williamson recognizes, there is an enormous difference between commonsense knowledge—that is, things that people genuinely know—from commonsense belief, which is what people merely think they know. The problem here, of course, is that without some method for reliably telling these two things apart, philosophy runs the risk of basing arguments and theories on false beliefs that people think they know to be true.

Second, appeals to commonsense in philosophy are a demonstrably unreliable method for distinguishing genuine knowledge (and truth) from mere belief (and falsehood). How do I know this? As Jason Brennan points out, philosophers disagree wildly over philosophical issues. Take any philosophical debate you like—consciousness, free will, morality, epistemology, justice, etc.—you will find a wide plurality of mutually incompatible arguments and theories. Because mutually incompatible claims cannot be true, it follows that virtually all philosophical arguments and theories are unsound, having false conclusions.

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Common sense can be regressive, wrongly presupposing the truth of prevailing prejudices.

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Third, better methods—specifically, scientific methods—have a long track record of refuting commonsense beliefs that people once (falsely) took to be knowledge. For example, it was once taken for granted, as commonsense knowledge, that the Earth is flat and stationary—yet we now know from scientific inquiry that the Earth is spherical and revolves around the Sun. The history of science is full of examples like this. Darwin’s theory of evolution, Einstein’s theory of relativity, quantum mechanics, etc.—all refuted commonsense beliefs about the world that people thought to be knowledge.

Fourth, to the extent that commonsense can get things wrong, basing philosophy upon it runs at least two further risks. First, commonsense can be regressive, wrongly presupposing the truth of prevailing prejudices. For example, in his 1680 work Patriarcha, British philosopher Robert Filmer used commonsense religious beliefs in his time to defend the divine right of kings, the view that monarchs rule with absolute, God-given authority. Second, to the extent that commonsense can be used to challenge prejudices, it can—if it is not adequately grounded in facts beyond commonsense—be recklessly utopian. For example, although Karl Marx gave what many take to be a strong commonsense argument against capitalism, Marx also claimed that a proletarian revolution to destroy capitalism will (somehow!) give rise to true Communism: a stateless way of human life without private property or exploitation. Suffice it to say, that prediction has never materialized. What has materialized from Marxist revolutions are rivers of blood: 20-62 million deaths in the Soviet Union, 40-77 million deaths in Maoist China, 1.3 million deaths in the Killing Fields of Cambodia, and so on. Capitalism may very well be deeply unjust—but unless we have more than commonsense to go on about the extent to which human beings can do better than capitalism, we run a serious risk of advocating utopian fantasies that do more harm than good.

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What are our philosophical options given the fallibility of commonsense, and which option is best?

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Science as an alternative to common sense?

Philosophers are sometimes admirably frank about the limitations of commonsense. Williamson recognizes its limitations—and, much like Brennan, Bertrand Russell writes:

Philosophy…is something intermediate between theology and science. Like theology, it consists of speculations on matters as to which definite knowledge has, so far, been unascertainable; but like science, it appeals to human reason rather than to authority…All definite knowledge—so I should contend—belongs to science; all dogma as to what surpasses definite knowledge belongs to theology. But between theology and science there is a No Man’s Land, exposed to attack on all sides; this No Man’s Land is philosophy.

The real question is not whether philosophical arguments based on commonsense are deeply fallible, but rather what the takeaway lesson is. What are our philosophical options given the fallibility of commonsense, and which option is best?

First, like Brennan, we might adopt an attitude of skepticism about philosophy, recognizing that ‘more likely than not, pursuing philosophy leads to false belief’. However, this is unattractive. Philosophers commonly take ourselves to be pursuing the truth—so if our methods are demonstrably unreliable at ascertaining the truth, this is a problem.

Second, like Williamson, we might recognize that philosophy is fallible, but hold that it is not unlike other disciplines in this regard, including the sciences, which also have a track record of getting things wrong. Most scientific theories in history have been disproven, after all. Yet, it is hard to sustain the claim that philosophy is similar to other disciplines. Unlike in the sciences, where there is increasing consensus on the truth of various theories and facts (for example, about facts of chemistry, biology, and basic physical forces), dissensus prevails in philosophy: there are lasting disagreements among experts on virtually every major philosophical issue.  

Third, we might try to adjust philosophy’s aims, contending that even if philosophy cannot reliably get at the truth, it can nevertheless advance human understanding. But this line runs into an obvious problem: if philosophy doesn’t reliably get at the truth, then how can we know whether whatever understanding it provides is valuable? False theories mislead people, after all—and if we are misled by a philosophical theory into believing false things, then that can amount to a harmful form of misunderstanding. For example, Thomas Hobbes’ political theory may help us understand human affairs. Then again, if Hobbes’s theory is false and we’re not able to reliably ascertain the respects in which it is false, we may be lulled into believing that we understand important things that we don’t. For example, Hobbesian realism about international relations—the view that moral norms do not apply to international affairs—has historically influenced US foreign policy. Yet, if Hobbesian realism is wrong (as I suspect it is), then the ‘understanding’ it provides of international relations may be false and harmful. To truly understand a phenomenon—and avoid potentially harmful misunderstandings—it seems like we need to know the truth about it.

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Because commonsense beliefs can be wrong, the sciences insist upon more rigorous epistemic standards: namely, that theories be based upon demonstrable intersubjective knowledge.

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This brings us to one final option: we might adjust philosophy’s methods. If our aim is to get at the truth (as I’ve suggested it should be), then—following the sciences—we should aim, whenever possible, to do better than rest on commonsense. How? Because commonsense beliefs can be wrong, the sciences insist upon more rigorous epistemic standards: namely, that theories be based upon demonstrable intersubjective knowledge. For example, it does not merely ‘seem true’ as a matter of commonsense that clocks slow down on fast-moving objects just like Einstein’s theory of relativity predicts; it is observably true in the sense that anyone can observe what happens to a clock when placed on a fast moving object (they do slow down!).

It is of course hard to approximate scientific methods in philosophy. In some areas of philosophy—such as abstract logic and mathematics—we can plausibly do so by invoking axioms that virtually everyone recognizes to be true (such as that 1+1=2). However, outside of logic and mathematics, the only way to approximate science’s epistemic standards is to do scientific (or ‘natural’) philosophy—that is, philosophy that draws on demonstrable scientific knowledge to explain and attempt to resolve philosophical problems.

Natural philosophy might enable philosophy do better than commonsense, when, for example, thinking about morality. One dominant view in moral philosophy today, defended by Derek Parfit and many others, is that moral truths are ‘non-natural’ and objective, depending in no way upon human psychology. Yet, many critics of this view (such as Sharon Street and myself) are skeptical, regarding it as a kind of secular religion, or ‘mere faith’ about morality. As a naturalistic philosopher, I’ve argued that we can do better by using science to challenge these and other features of moral commonsense.

Naturalistic approaches to explaining and resolving philosophical problems are of course controversial—and there have been ongoing disagreements about these very matters between rationalist and empiricist philosophers across history. And, of course, only time will tell whether naturalistic philosophy can live up to the promise of the sciences, bringing clarity and consensus to philosophical problems where commonsense does not. However, in the end we must compare each approach, and as we have seen here, science-based natural philosophy has obvious virtues that—from the standpoints of truth and understanding—appear to be worth striving toward.

References

Arvan, Marcus (2020). Neurofunctional Prudence and Morality: A Philosophical Theory. New York, USA: Routledge.

Arvan, Marcus (2021). The Normative Stance. Philosophical Forum 52 (1):79-89.

Bourget, David & Chalmers, David J. (2014). What do philosophers believe? Philosophical Studies 170 (3):465-500.

Hobbes, Thomas (1651). Leviathan or The Matter, Forme and Power of a Commonwealth Ecclesiasticall and Civil.

Parfit, D. (2011). On What Matters: Two-Volume Set (Oxford: Oxford University Press)

Russell, Bertrand (1945). A History of Western Philosophy. New York: Simon and Schuster.

Street, Sharon (2016). Objectivity and Truth: You’d Better Rethink It. Oxford Studies in Metaethics 11.

Williamson, Timothy (2018). Doing Philosophy: From Common Curiosity to Logical Reasoning. Oxford University Press.