Friday, October 8, 2021

Deceit and Double Effect

Suppose you inform me of something true, p, and as a result I come to believe it. Then very likely you’ve deceived me about something!

For there is surely some falsehood q that I believed previously with a high confidence. But presumably I did not believe the conjunction p&q before I got your information, since I didn’t believe p. But now that you’ve informed me of p, I am likely to believe p&q, and yet that is a falsehood.

Sometimes this argument doesn’t work (maybe sometimes I believed p&q when I didn’t believe q, and maybe sometimes my belief in p is sufficiently marginal that I still don’t believe p&q), but most of the time it does.

This means that we are typically deceiving people all the time in conversation! This sounds bad, unless we make a distinction between foreseeing and intending. You can foresee (now that you saw the above argument) that whenever you inform me of something this is likely to deceive me about something else. But merely foreseen deceit counts for very little morally as long as you don’t intend the deceit.


SMatthewStolte said...

In order for your argument to work, your false belief that p&q has to count as an additional harm on top of your false belief that q. But if that is the case, then your believing that p&q is not the only harm I foresee to result from telling you that p. You are also probably going to believe that q&p&p, as well as q&p&p&p and 1&p&p&··· and so on.

Depending on what it means to believe a proposition, we might be forced to say that, by informing you that p, I have foreseeably caused you an infinite amount of harm. So even if I didn’t intend this, I had better have some very strong reasons for doing so in order to outweigh this harm. And I guess the amount of foreseeable good would be infinite too (since you believe that p&p as well as p&p&p and so on). But that just seems like the wrong way to analyze what is going on.

One way to try to get out of it would be to limit beliefs to things that are actually thought. And since you will not actually have an infinite number of thoughts, the harm from telling you that p would definitely not be infinite. But that still seems like the wrong way to analyze the situation.

A better way would be to put a rule in place about how we count the harms of false beliefs. We’d need some way of making sense of a claim that people make all the time—namely, the claim that something can be partly true and partly false. So the belief that p&q is partly true (p is true) and partly false (q is false). And then we would have to say that we aren’t allowed to double-count the harm of believing that q.

Alexander R Pruss said...


That "and so on" doesn't go on forever, as I don't believe infinitely many propositions.

SMatthewStolte said...

I thought you might not believe in infinitely many beliefs. That’s why I introduced a hand-wavy argument in the third paragraph. It still seems to me that, in typical cases, when I inform someone about some true proposition, I do that person no harm at all. Granted, there are plenty of cases that are not typical, because sometimes I might cause hurt feelings. But in such cases, I have a reason (perhaps a very weak reason) to apologize, just as I have a reason to apologize when I accidentally bump into someone walking around a corner. Yet it seems like I have no reason at all to apologize in typical cases of informing a person that p.

Alexander R Pruss said...

That's reasonable. But be it harmless or not, deceit still happens.

There is, of course, such a thing as on balance harmless deceit, even on balance epistemically harmless deceit. Thus, when we teach science, especially but not only at lower levels, we expect our listeners to acquire all sorts of false beliefs along with the true ones (e.g., children when they first hear about particles come to think they are small hard round objects). Such misunderstandings are, we hope, balanced out by the more important truths that are conveyed.

Nik Breiner said...

Hi! I’m interested in the notion of deceit assumed by the argument. Obviously one place that comes into play is at the end, where it’s assumed that unintentional-but-foreseen deceit is deceit. I wonder if that’s right. (Can one deceive without intending to deceive? …perhaps.) But set that aside.

The earlier part of the argument seems to suppose that someone is on the hook for deceit if they engage in some communicative act that brings about the addressees’ having a false belief. That seems wrong to me.

Suppose I inform you that P, and you come to believe P. Now suppose someone else later in the day informs you that people who inform others that P are highly likely to have some special property F (they are especially kindhearted, say), and so you come to believe (mistakenly) that I am/have F. It seems my informing you of P is a partial cause of your believing that I am F, and so my informing you of P is a partial cause of your having a false belief. But it seems crazy to say that I’ve deceived you—and this despite the fact that my informing you of P plays a causal role in your coming to have a false belief.

There are, of course, various disanalogies between this example and the case you envisioned. Still, I think the case shows that the idea of deceiving is more demanding than that of just causing (in a partial way) someone to have a false belief. This is relevant because if the notion of deceit is indeed more demanding, then we could say, of the case you raised: the person informed you that P, which lead to (played a causal role with respect to) your believing P*Q, yet nevertheless they did not deceive you with respect to the conjunction P * Q. This position would likely appeal to some more robust notion of deception—perhaps one that accepts this as a constraint: someone deceives another with respect to some proposition P only if they assert (or perhaps convey via implicature) P. Something like that might be able to get us the desired result about the ‘elementary teachers deceive students about atoms’, yet it would also suggest of the case you gave (P leading to false belief P and Q) that they did not deceive you--for they obviously did not assert (or convey) P*Q.

In short, deceiving someone about P seems to involve trying to get someone to believe P, or at least representing oneself as believing P—but neither of these transpires with respect to P*Q when a person informs you that P.

Alexander R Pruss said...

I think you're right that deceit requires more than just causation of false belief. But it does not follow that it requires intention to cause a false belief. An in-between position would be that deceit requires foreseeing that one will cause false belief.

Maybe we should distinguish between an action deceiving one and a person deceiving one? Say, a school teacher asks a question in class, and Alice happens to raise her hand to ask to go to the bathroom. I think we would be happy to say that Alice's raising her hand deceived the teacher into thinking Alice had an answer. But perhaps we wouldn't say that *Alice* deceived the teacher.

However, I think we would be happy to say that Alice *unintentionally* or *accidentally* deceived the teacher.

My feeling is that words like "deceived" or "killed" normally *implicate* intention, so that we need to cancel the implicature by adding "unintentionally" or "accidentally" or the like.

Alexander R Pruss said...


I think this suggestion is not right:

"someone deceives another with respect to some proposition P only if they assert (or perhaps convey via implicature) P"

Deceit is way broader than linguistic or even symbolic behavior. Some examples: feinting in sports or a fight, using dummy tanks ( ), wearing a disguise, etc. These cause false belief, but they do not do so by conveying a proposition in assertion or implicature or anything like that. They simply provide *evidence* for a false proposition.

In fact, it is usual to count many animal and plant behaviors as forms of deception, though in some cases it may be only an analogical sense. I am inclined to think that in the primary sense of "deceive", one is causing something like a false belief, but in some of the animal and plant cases, there may be no beliefs involved, but mere behavior.

Nik Breiner said...


That is a great point: there is deceit with actions, and not just speech. Thank you!

That said, what do you think of this: most of those cases you cited involve more than just causing a false belief, or even causing a false belief by providing evidence for that false belief; they involve *representing* oneself as being a certain way that one is not. So the person who "dives" in soccer (fakes their being tripped) represents themselves as having been illegally tripped; the army that deploys dummy tanks represents themselves as prepared for a possible enemy strike, or perhaps as anticipating an enemy strike in a certain location.

If this misrepresentation is an element in all deception, then there'd be a question about how (or whether)to integrate this element with the 'causing one's addressee to have a false belief' element. Is it that the misrepresenting-one's-self amounts to nothing more than presenting misleading evidence? Or is it the other way around, i.e. that in deception, one causes one's addressee to have a false belief (or provides evidence for a false belief) *by* representing themselves in a way they are not? (or, more generally, as representing *X* as being F, since perhaps I could deceive someone about the location of a treasure by representing that location falsely, though even here things might be reducible to representing oneself in a certain way, i.e. as believing that the treasure is in a certain location).

I do think that 'representing oneself as being F (when one is not)' is different than merely 'causing X to have a false belief.' Paul and Barnabas (inadvertently) caused the Lyconians to believe they were Hermes and Zeus, but they did not represent themselves as being Hermes and Zeus. If I walk into a bar and take a drink, I might inadvertently and unbeknownst to me cause a spy to believe I am their mark; but I'd not represent myself as being that person (contrast the case of my putting on a mask and garb so as to appear to be their mark).

What exactly the nature of 'representing oneself (or some object) as being F' is, I am not sure! But I am inclined to think that deception should be understood in terms of it. Deception involves *a particular way* of causing (or trying to cause) one to have a false belief, and not merely causing them--in any old way--to have such a belief.

Alexander R Pruss said...


I hadn't noticed the element of misrepresenting one's self that is common to all these cases.

But suppose you and I are competing in a hunt for the white stag. I see some stag footprints leading in one direction. I erase them and make fake stag footprints leading in the opposite direction. It seems to me that I am trying to deceive you about where the stag is going, but I am not misrepresenting myself. Am I misrepresenting the stag, as in your treasure case? That seems wrong: my act of laying down false stag footprints is not a representative act. It is simply an act of putting down misleading evidence.

Compare putting down a false scent for an animal to follow. This is a form of deception. But we're not representing anything to the animal.

I am not sure that intentionally inducing a false belief is needed for intentional deception. Suppose law enforcement thinks I'm 99% likely to be guilty of a particular crime, but I figured out a clever and dishonest ruse that would lower that credence to 30%. I don't expect to, or even intend to, cause them to believe in my innocence, but I do intend their credence in my innocence to rise from 1% to 70%. There is deception here.

All in all, it really does seem that in the case of intentional deception of fellow humans, it's enough if we intend misleading evidence resulting in a significant change of credence.

I wonder if deception has to go through evidence. Suppose that I am a neurosurgeon, and while doing surgery on your brain, I tweak some neurons to make you have the belief that you have promised to give me all your money. Have I deceived you? (Maybe, though, the possession of the belief is itself evidence for it?)

Nik Breiner said...

These are great points and examples! I agree they are non-representational, and they do seem to count as cases of deception.

Here's another thought about deception: it's exploitative.

I know you are inclined to believe me if I assert P; so I exploit this fact by asserting P (since it's to my advantage that you believe P).
One army knows another will believe (or have rather high credence with respect to) P if the latter sees a bunch of the former's tank-like things in a certain place.  So it exploits this fact by putting tank-like things there (since it's to their advantage...etc)
Same goes for the white stag case: you know I am inclined to make certain inferences on the grounds of their being (fake) stag footprints in a certain place.  So, you exploit this fact...

If this exploitative characteristic holds across the board, it could be why  'foreseeing false belief' is a necessary element of deception.  'Exploitation' (at least in the above cases) seems to involve grasping in advance how one would respond (doxastically / epistemically) to a certain action/state.
This exploitative character is helpful for thinking of the neuroscientist case: the neuroscientist exploits a neurological-doxastic process: tinker with neuron x, induce (through a kind of brain-mind interaction) belief y.  This is different than the previous cases, which exploit epistemic-doxastic processes: present evidence x, induce (through a rational, not merely causal, process) belief y.

Is this understanding of deception as exploitative completely consistent with the claims you were making about deception? I'm not sure. It might turn on whether you can 'intend misleading evidence' without exploiting (or trying to exploit) some fact/likelihood about how one will respond to certain fact/actions (i.e. evidence).