We all think we believe what we believe for good reasons – especially philosophers. However, as figures such as Nietzsche, William James and Iris Murdoch have suggested, what we believe may be influenced far more by our psychology and life experiences, rather than by logic and reason, writes David Bryce Yaden and Derek Anderson.
How do philosophers come to endorse one view over another? One might imagine an impartial analysis of the merits of various arguments. Indeed, we don’t doubt that this accounts for the majority of the process. But what other influences––perhaps more psychological––should we consider? That is the question that we explored in our new paper, “The Psychology of Philosophy.” 
One potential influence on a given philosopher’s views may be their personality or other psychological traits. Does a philosopher’s disposition relate to complicated philosophical views, such as whether free will exists, whether one endorses deontological or consequentialist ethical views, or whether morality and aesthetics are objective or subjective? These questions are not new.
In Beyond Good and Evil, in a section called “The Prejudices of Philosophers” Nietzsche writes:
"They all pose as though their real opinions had been discovered and attained through the self-evolving of a cold, pure, divinely indifferent dialectic (in contrast to all sorts of mystics, who, fairer and foolisher, talk of "inspiration"), whereas, in fact, a prejudiced proposition, idea, or "suggestion," which is generally their heart's desire abstracted and refined, is defended by them with arguments sought out after the event…It has gradually become clear to me what every great philosophy up till now has consisted of--namely, the confession of its originator, and a species of involuntary and unconscious auto-biography”
Does a philosopher’s disposition relate to complicated philosophical views?
In Pragmatism, William James writes:
“The history of philosophy is to a great extent that of a certain clash of human temperaments. Undignified as such a treatment may seem to some of my colleagues, I shall have to take account of this clash and explain a good many of the divergencies of philosophers by it. Of whatever temperament a professional philosopher is, he tries when philosophizing to sink the fact of his temperament. Temperament is no conventionally recognized reason, so he urges impersonal reasons only for his conclusions. Yet his temperament really gives him a stronger bias than any of his more strictly objective premises.”
In The Sovereignty of Good, Iris Murdoch writes:
“To do philosophy is to explore one’s own temperament and yet at the same time to discover the truth. It seems to me that there is a void in present-day moral philosophy…A working philosophical psychology is needed...”
One might wonder whether it is significant that each of these philosophers who drew special attention to the role of temperament in philosophy also had substantial interdisciplinary expertise or training. Before writing now classic works of philosophy, Nietzsche was a professor of philology at the University of Basel with a focus on historical texts from Greece. James had a medical degree and was a founder of empirical psychology before becoming a professor of philosophy at Harvard. Murdoch taught philosophy at Oxford and was an acclaimed novelist.
The theme of these speculations from these interdisciplinary philosophers is that our real reasons for believing are not what we take them to be. Many philosophers act as if they are simply being rational, following the evidence and arguments where they lead with the disinterested clarity of an objective investigator. But for Nietzsche, James, and Murdoch, as well as many others to be sure, this belief in our own objective rationality is suspect. If our temperament or “our heart’s desire” is guiding our philosophical worldview, then our commitment to pure rationality is partly a refusal to acknowledge our real reasons for believing.
If our temperament or “our heart’s desire” is guiding our philosophical worldview, then our commitment to pure rationality is partly a refusal to acknowledge our real reasons for believing.
Our own humble contribution to this topic emerged out of an interdisciplinary conversation among friends that stretches over many years, beginning in our undergrad years. We, a psychologist (David Yaden) and a philosopher (Derek Anderson), began discussing the reasons why people in our philosophy and cognitive science clubs seem so quickly attracted to one view over another––even after very little exposure to the relevant arguments or evidence. Of course, there are important sociological issues to consider (i.e. what professor you happened to have or book you recently read), but we wondered whether there could also be psychological reasons to account for the attraction one feels to a particular view.
It was years before we were able to return to this question. We both first needed to get our doctorates in psychology and philosophy. But over this period of time, two important things happened in the field of philosophy. The first was that a new branch of philosophy was formed, called Experimental Philosophy (“x-phi” for short). This field uses methods from psychology to address philosophical questions. The idea is to get up off the proverbial armchair and to collect data – the primary symbol of x-phi according to Josh Knobe is a burning armchair . X-phi focuses on peoples’ intuitions on various thought experiments, to see whether or not they differ across cultures or between professional philosophers and non-philosophers. Here is an example of a common thought experiment (this one was originally proposed by Bertrand Russell and later Edmund Gettier created closely related thought experiments which upended the study of epistemology for forty years):
Imagine a person who looks at an analog clock. The hands of the clock display the time 3:00pm. On the basis of this, the person comes to believe it is 3:00pm. Since looking at a clock is a good source of justification for knowing the time, the person seems to be justified in their belief. Let’s also assume that it really is 3:00pm. But unbeknownst to the person, the clock is actually broken. It always points to 3:00pm. It is only a strange accident that the person happened to look at precisely the right time to form a true belief.
Does this person know that it is 3:00pm? Many philosophers have judged that, intuitively, the person does not know. If this intuition is correct, then knowledge must require more than a true justified belief (which is the traditional analysis of knowledge). But does everyone share this intuition, or is there variability in people’s judgments? If there is variability, what explains this? These are empirical questions which x-phi has been concerned to answer.
Our focus is somewhat different. Like Nietzsche and James, we are interested in the considered views that philosophers adopt, rather than their intuitions about thought experiments like the one above. We are interested in people’s beliefs about, for example, whether god exists or not, whether freewill exists or not, or whether morality is subjective or objective. Specifically, we are interested in whether psychological factors predict whether people hold one view instead of another when it comes to philosophy. We are not so much focused on people’s intuitive judgments about thought experiments.
In order to begin to answer these kinds of questions, we devised a survey by which we could look for correlations between philosophical views and psychological factors. Happily, a survey of philosophical views was created by David Bourget and David Chalmers , called the PhilPapers Survey, that captured 30 different philosophical views––here are the first 10:
1. A priori knowledge: yes or no?
2. Abstract objects: Platonism or nominalism?
3. Aesthetic value: objective or subjective?
4. Analytic-synthetic distinction: yes or no?
5. Epistemic justification: internalism or externalism?
6. External world: idealism, skepticism, or non-skeptical realism?
7. Free will: compatibilism, libertarianism, or no free will?
8. God: theism or atheism?
9. Knowledge: empiricism or rationalism?
10. Knowledge claims: contextualism, relativism, or invariantism?
Many of these are technical terms used by professional philosophers. Readers who are interested in taking a non-technical version of this survey with questions designed so that non-philosophers can understand them, they can do so here.
Specifically, we are interested in whether psychological factors predict whether people hold one view instead of another when it comes to philosophy.
While doing our doctoral training, Derek sent a paper reporting the findings from this survey to David. The potential of these questions as self-report items was immediately obvious to David. In the article, “What do Philosopher’s Believe.”  David Bourget and David Chalmers provided correlations with demographics, but, importantly for us, they did not administer any psychological measures. We realized that we could address our old question about philosophical views and temperament by re-administering the PhilPapers Survey to professors of philosophy (as well as some grad students and postdocs) with the addition of measures of psychological traits. Here are some of the psychological traits that we measured:
- Personality – Openness to Experience, Conscientiousness, Extraversion, Agreeableness, Neuroticism
- Numeracy – competence with and interest in using numbers, reading about data, and performing calculations
- Substance Use – use of marijuana and psychedelic substances
- Experiences – reporting have had a self-transcendent experience (feelings of unity and ego-dissolution)
- Mental health – satisfaction with life and depression
We then correlated the philosophical views from the PhilPapers Survey with the psychological traits. Because we were making so many comparisons, we needed to statistically correct for this, so the results that we report needed to pass a very strict threshold to be considered “statistically significant.” Interestingly, we did not find statistically significant correlations with demographics or personality, although further research is needed before drawing any conclusions from this finding.
But, we did find some correlations between philosophical views and psychological traits. We found, for example, that:
- Belief in determinism (no free will) is associated with lower satisfaction with life and higher depression
- Belief in consequentialism is associated with numeracy (interest in numbers)
- Belief in non-classical logic (the idea that something can be both true and false) is associated with having had a self-transcendent experience of ego-dissolution
- Beliefs that morality and aesthetics are subjective (“in the eye of the beholder”) are associated with marijuana and psychedelic use
- Many other findings, which can be read in our paper  and especially its supplement. 
It is crucial to understand that these correlations don’t tell us anything about causality––that is, we can’t tell whether the psychological trait is impacting one’s philosophical views or whether the philosophical view is impacting one’s psychological traits. Also, our findings come from professional philosophers, so it’s not yet clear how these findings do or don’t generalize to people in general.
While much more scientific study and philosophical analysis is yet required, we nonetheless believe that the empirical results from the psychology of philosophy provide a kind of outside perspective on one’s self.
What would Nietzsche, James, and Murdoch have to say about these findings? We don’t know, but we personally believe these findings are worth knowing. To be honest, we don’t yet fully understand what this means for philosophy. One idea is that philosophers who know that some of their psychological traits predict certain philosophical views might somehow take these findings into account while reading the philosophical arguments for various views. For those with certain psychological dispositions to adopt certain kinds of philosophical views, knowing about these findings could perhaps help philosophers to avoid a systematic bias. But perhaps not––maybe these findings are best ignored by philosophers when they are considering arguments for philosophical views and are only of scientific interest. Philosophy may be a personal journey, and it may not be relevant to know what is statistically likely for groups while developing your own worldview. In that case, maybe philosophers should even be careful to avoid reading about our findings! Lastly, these findings may allow us to understand better the psychological impact and implications of holding certain philosophical views on one’s life. At this point, the only thing that is clear to us is that many questions remain.
While much more scientific study and philosophical analysis is yet required, we nonetheless believe that the empirical results from the psychology of philosophy provide a kind of outside perspective on one’s self––perhaps adding a new empirical and quantitative component to the maxim, “know thyself.”
Peter Hacker explores whether intuition or reason should guide us in our decision making.
 The Psychology of Philosophy, David Bryce Yaden and Derek Anderson, 2021, https://www.researchgate.net/publication/351156867_The_psychology_of_philosophy_Associating_philosophical_views_with_psychological_traits_in_professional_philosophers
 The Ironic Success Of Experimental Philosophy, Tania Lombrozo, 2018, https://www.nhpr.org/post/ironic-success-experimental-philosophy#stream/0
 What Do Philosophers Believe?, David Bourget and David J. Chalmers, 2013 https://philpapers.org/archive/bouwdp
 Supplement to ‘The Psychology of Philosophy’, David Bryce Yaden and Derek Anderson, 2021, https://www.researchgate.net/publication/351229767_psych_o_phil_supp_cphp_a_1915972_sm2624pdf