Week 2: Psillos

Psillos critically examines the epistemology of Bas van Fraassen, not with regard to any specific questions about realism and antirealism, but with its implications for rationality. In particular, he takes issue that van Fraassen’s conception of rationality has no compelling story about prior beliefs, ignores the content of belief, unfairly rejects IBE,  and calls rational what we really ought to be able to call irrational.

Background: Sailing between Bayesianism and Tradition

To understand van Fraassen’s view of rationality, let’s first get a handle on the positions that he is trying to mediate between. 

Traditional Epistemology: 

Traditional Epistemology is not a particularly well defined position per se, but the relevant features of it for this debate is that it suggests that we are rationally obligated to follow ampliative rules in our belief formation. A rule is ampliative if it (supposedly) allows for one to derive conclusions that extend beyond the premises. A way to think of it is that they are arguments that can be good but not sound in the strict sense. In particular, the ampliative rules in question are Induction and Inference to Best Explanation (IBE). Induction is the inference to a general law from a sufficient set of particular instances (eg. every day of my life, the sun has risen, thus the sun will rise everyday) and IBE is the belief in the explanation that best suits the evidence (eg. all of my electronics stopped working at the same time, so the power is out). This is especially important because in traditional epistemology, since for a belief to be rational, it must be justified, which leaves nothing to choice. Even though these inferences are not deductive, we say that it is rational to make them, and more saliently, irrational not to

Bayesian Epistemology:

Bayesian Epistemology designed to put induction in purely logical terms. Bayesians do that by focusing on beliefs not as binary belief and disbelief, but as a range of credences one can hold towards a proposition. In doing so, inductive inferences can be treated with the same level of deductive rationality as ordinary propositional logic. There are two views on rationality within Bayesianism: synchronic and diachronic. Synchronic Bayesianism constrains rational belief by whether or not beliefs can be held at the same time coherently. The corresponding rule in ordinary logic is the principle of noncontradiction. Since credences are a range, irrationality (to a synchronic bayesian) is demonstrated with a Dutch Book argument. These show that if you were to place a series of bets that correspond perfectly to your beliefs at the same time, you would suffer a loss (imagine a situation in which a coin would be flipped 100 times and you bet $150 dollars that it would land heads 75 times and tails 75 times; you would necessarily lose $50). A Bayesian can go another step and constrain the rules by which beliefs must be updated. This is Diachronic Bayesianism. Diachronic Bayesians constrain rational belief by whether or not one changes their belief in accordance with evidence (on top of already having them cohere in the synchronic sense). This corresponds to a belief in ordinary logic that if you believe that P and that  P-> Q, you are rationally obligated to believe Q. This is also demonstrated with a Dutch Book argument (imagine a situation in which you believe that there is a 1% chance that a coin is rigged to always land heads, if you were asked to bet (out of $100) on whether the coin will land heads, you should at first bet ~$51, but if I then flipped the coin a thousand times and they all landed heads, you would be irrational to not start betting higher). This process of updating beliefs is called conditionalization and follows the form Pr(H) = Pr(H|e) upon being shown evidence e for hypothesis H. Note that these rules are markedly non-ampliative, but still allow for our inductive intuitions to be satisfied. This has the benefit of avoiding the problem of induction, but the drawback of not having much of a story about how we get our initial beliefs.

Some argue that since no one is consciously doing said probability math in their heads whenever examining any evidence, it is unfair to hold this as a meaningful picture of rationality. Do you think that is a fair argument? If not, how do we provide a readily applicable concept of Bayesian rationality to ordinary people?

Voluntarism (BvF’s view):

Van Fraassen’s voluntarism attempts to find a comfortable middle ground between these two views in epistemology by introducing our will in the formation of our beliefs. He argues that it is rational to hold beliefs that extend beyond evidence (use ampliative inferences) but he does not hold that beliefs that extend beyond evidence are rationally obligatory. Rather he believes that they are permissible, so, by our will, we may believe them. 

BvF defines four epistemic principles to lay out exactly how his view differs from the others.

  1. There can be no independent justification to continue to believe what we already find ourselves believing
  2. It is irrational to maintain unjustified opinions
  3. There can be no independent justification for any ampliative extrapolation of the evidence plus previous opinion to the future
  4. It is irrational to extrapolate ampliatively without justification

Belief in all four of these is tantamount to skepticism, since it says that we need to justify our beliefs but cannot justify our initial beliefs, nor can we justify extending our beliefs from our prior, irrational beliefs. Bayesians avoid this by denying premise 2. Since Bayesians do not concern themselves with justification, they can sustain having credences and changing them (according to evidence) without needing a story for what justifies them initially. Van Fraassen goes another step and also denies the need for justification for extrapolation (he rejects premise 2 and 4). Thus, van Fraassen believes that we are neither rationally obligated to justify our initial beliefs, nor are we rationally obligated to contitionalize our beliefs on the evidence. 

Now, not just any belief is permissible, but note the important distinction between rationality deciding what one can believe as opposed to what one must believe. The bounds for what one can believe are provided by three items. (1) Prior opinion (2) logical and synchronic (not diachronic!) coherence (3) does not a priori preclude the possibility of vindication.

Logical but nonetheless Irrational: Psillos’ arguments against Bayesianism

Before getting into Psillos’ arguments against voluntarism. Let’s note his argument for why Bayesianism leaves much to be desired for a theory of rationality.

  1. Bayesians believe that our initial beliefs need not be justified by evidence, only that they must be responsive to evidence so that credences can be recalculated
  2. It is irrational to believe a claim without evidence
  3. Bayesians are being irrational when accepting a new belief

What Psillos gets at with this argument is that the strict non-ampliative nature of Bayesianism leaves a gap in explanation for how and why one would go about acquiring new beliefs or deciding that a new piece of evidence is worth considering. He makes the example that there is a lot of evidence that the earth is round, and a little evidence that the earth is flat. Yet, one could, without transgressing any Bayesian rules of rationality, ignore all of the former and believe that the earth is flat. 

Is this a problem for the Bayesian? Can rationality only refer to how our beliefs hang together, or must it make reference to the content of our beliefs? In other words, can it be the case that any belief is rational so long as it is in the right context?

Saving the bacon or burning it? Psillos’ arguments against van Fraassen

Focusing on the third item with regard to how rationality bounds the range of possible beliefs, van Fraassen argues that our beliefs are constrained by our prior beliefs. These prior beliefs are sensitive to an external factor, namely truth. That is to say that even though we choose our beliefs, that does not change the fact that some beliefs can be right upon investigating the relevant facts about the world. Psillos argues that van Fraasen’s voluntarism makes the error of ignoring the content of belief, when it is still a necessary consideration for rationality.

  1. Some beliefs are decidably true or false and likely to be false upon investigation
  2. It is irrational to hold beliefs that, upon checking, are likely to be false
  3. Some beliefs are irrational to hold, regardless of other beliefs
This argument is a bit strange to me (and may be an incorrect reading) as it seems like it is no different from the call for synchronic coherence. Premise two is doing a lot of work by declaring the belief in question to be likely to be false. If we already believe that the belief is likely to be false, would we not be susceptible to a Dutch Book argument? This argument seems to assume that we can know beforehand how likely it is that a belief can be vindicated.

Psillos next argues that BvF’s view does not have an adequate story about how evidence can be incorporated into one’s belief-corpus.

  1. Having true beliefs aids us in our goals
  2. Not pursuing our goals is irrational
  3. Evidence aids in our ability to have true beliefs
  4. It is irrational to not conditionalize on evidence
We may say that it is unwise to not pursue our goals, but is it correct to say that it is irrational?

Psillos then defends IBE against an argument that van Fraassen provides. Van Fraassen argues that if one uses IBE they are susceptible to a Dutch Book situation, since they are providing an unfair probability bonus to a hypothesis H because it satisfies the “best” criterion, which may not necessarily connect to the probability of H being true. 

Psillos argues that one does not run into this problem if they apply IBE consistently before and after learning that H is the best explanation. 

Lastly, Psillos argues that BvF’s voluntarism permits obvious cases of irrationality. Namely…

  1. Cases where one disregards evidence that pertains to the truth or falsity of their beliefs.
  2. Cases where one changes between two permissible beliefs for arbitrarily reasons
  3. Cases where one could refute their own belief with another one of their beliefs
Are these cases irrational? Who gets to decide which evidence pertains to their beliefs? Who gets to decide which reasons are arbitrary? 

6 thoughts on “Week 2: Psillos

  1. Phin Choukas

    I agree with Psillos’s critique of Van Frassen at the end concerning simultaneously competing beliefs. As Nate points out, the Mary example seems to poke a hole in a solely coherence-based rationality. Also, the flat earth example seems to show that coherence alone cannot satisfy rationality as it ignores taking all evidence into consideration. Moreover, this leads us to believe that Van Frassen’s central dictim, that “rationality is only bridled irrationality,” is too weak. Thus a lack of consideration for the truth-value of prior beliefs seems to be a big problem to me, although I cannot pretend to fully understand everything going on here!

  2. Rebecca Amen

    Thank you, Farhan, for this outline! It’s really helpful!

    I am interested primarily in Psillos’ evaluation of van Fraasen’s voluntarism as a potential surrender to relativistic perspectives of truth. This seems to have salient connections with your last question about circumstances in which irrationality is permitted under van Fraasen’s framework. I’d be troubled to see how these circumstances do not require some sort of truth-relativism, which is why I am not satisfied when Psillos claims that van Fraasen “denies the premises of the relativist argument.” This is as van Fraasen sees prior opinion as subject to some constraints of truth. But to disregard evidence that substantiates a non-belief, or to disregard evidence that negates a present belief, appears inherently relativistic to me. Additionally, an arbitrary and at-will (if those two terms are not oxymoronic) oscillation between two permissible beliefs belongs in that sphere of relativism, too, for it holds the air of “anything goes.” Indeed, if there were to be a foundation of prior opinion subject to limitations of truth, then how can switching between beliefs—presumably that hold some element of contradiction—be permissible except in a relativistic view? This goes with the idea of beliefs in tension, or cognitive dissonance. Resolving cognitive dissonance is perhaps an exercise in defeating relativism. If two contradictory beliefs can be held in conjunction, is there not some tenet of relativism enabling that?

    I would ask, I suppose, for some clarifying discussion as to how van Fraasen’s conception of voluntarism does not allow for relativism to rear its head. If foundational prior opinion is constrained by truth, how are van Fraasen’s cases of irrationality listed in this outline permissible under voluntarism?

  3. Kenzo Okazaki

    Thanks Farhan!

    I am interested in the argument against BvF’s voluntarism, especially regarding the premise:
    It is irrational to hold beliefs that, upon checking, are likely to be false
    In response to the quesiton you pose (partially), I understood that the notion of probability that enters the phrase “likely to be false” rests upon an evaluation of available evidence. Thus one would not already believe that their beliefs are likely to be false but would rather have to revise it based on new evidence (it seems that the reply Psillos offers to BvF’s argument against IBE would resolve the Dutch book issue, though, I am not sure that I fully understand the concept yet).

    My understanding of this premise, though, leads me to some dissatisfaction with it. Indeed, if one held a belief that was subject to revision by consulting evidence relating to the content of that belief, this would be influenced, in turn, by other beliefs (say, for example, that the government is concealing evidence). This points to the coherentist view of rationality that BvF responds to at approx p. 155. Am I correct in understanding that this premise is only true if rationality requires more than coherence?

    In the sum of the above comments, I share your puzzlement at the supposition that one can know beforehand that their belief is likely to be vindicated.

    Now, my (potentially mistaken) reading of the above argument beings me to the section where you ask if rationality is determined by outside factors rather than coherence. I am thinking of this in relation to Wednesday’s class. If we take an epistemic policy as a stance, then it is the governing principle of what is rational as a coherentist paradigm. Can this be divorced from probability as discussed in this article? that is, if our epistemic policy prompts us to believe unlikely things (given available evidence) does it escape Psillos’s criticizm of Bayesian epistemology (that it does not say when we should revise our beliefs)? Perhaps the reply is simply that if a stance does not offer a good guide to truth it is irrational to hold it.

  4. Nathan Obbard

    Hey, great write-up Farhan! I’m interested in the cases you mention near the end, such as that of Mary, who flip-flops between p and not-p, neither of which is precluded by a negative formulation of evidence acceptance. The power of this example, I think, is in its revealing of strong prior notions of what even counts as ‘rational’ in the first place, and how, as Psillos notes, these notions are at least partially normative – those of us who find this example a persuasive refutation of solely coherence-based model of rationality agree that we do so because we share a conception of rationality which does not allow for so-called ‘bad practices.’ That is, being rational entails not behaving in ways which have a ‘bad’ relation to truth, a question which goes above and beyond whether one’s thought processes are consistently following logical rules.

    I think grasping the role of normative heuristics in our ascription of rationality helps to trim some otherwise-thorny questions regarding how evidence ought be factored into our definition of rationality, and makes it clear that ‘rationality’ is not actually, for most people, a purely descriptive term, but one which captures a certain way of interacting with the world and its contents that is in some sense virtuous or worth seeking out for moral reasons.

  5. Peter Huggins

    I think this is where we’re supposed to do this…

    Great summary and interesting readings, Farhan!

    I agree, in some degree, with both Van Frassen and Bayesianism. For Bayesianism, I think that the ability to believe things without evidence is important, especially if that evidence is deemed irrational. While I’m not advocating for a Flat Earth theory, (in any way, shape, or form. The Earth is clearly a sphere) there are many scientific theories that started out as irrational beliefs. For example, think of Galileo. While he compiled evidence, people still called him irrational and crazy.

    However, the question that I generated from this reading was this: what if there is no evidence to either side of an argument? What if both sides are deemed irrational? I think of the existence of God as a great example. While there is obviously no scientific proof that God exists, there is neither any evidence to suggest that God does not exist. Therefore, according to Van Frassen, both sides are irrational. How do arguments with conditions such as these work?

    Side note: I think that Bayesianism is a great depiction of how most people think. It describes the thought process as it truly is, for most people. Van Frassen, however, describes an ideal thought process, one which very few people would utilize in their everyday lives. If everybody operated like Van Frassen prescribes, the world would be a lot more predictable.

  6. Nam Nguyen

    I had a question from the reading that was summed up in the section “Logical but nonetheless Irrational: Psillos’ arguments against Bayesianism”. In this section, Psilos argues that Bayesian rules would not be violated if one were to believe that the earth is flat. However, this seems to violate the conditions of Bayesian epistemology which states that your beliefs (or the credence you assign to them) should be altered based the evidence available. Ignoring the evidence that the earth is round in favor of increasing credence in a belief that the earth is flat seems to violate this rule (premise 1 in the summary provided). It seems that in the case where one ignores the evidence that the earth is round in favor of a conclusion that the earth is flat, they are not responsive to the evidence available at hand.

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