Here are the slides from my discussion of Nancy Reid today at BFF4: The Fourth Bayesian, Fiducial, and Frequentist Workshop: May 1-3, 2017 (hosted by Harvard University)

# C.S. Peirce

## “Fusion-Confusion?” My Discussion of Nancy Reid: “BFF Four- Are we Converging?”

## Peircean Induction and the Error-Correcting Thesis (Part I)

Today is C.S. Peirce’s birthday. He’s one of my all time heroes. You should read him: he’s a treasure chest on essentially any topic, and he anticipated several major ideas in statistics (e.g., randomization, confidence intervals) as well as in logic. I’ll reblog the first portion of a (2005) paper of mine. Links to Parts 2 and 3 are at the end. It’s written for a very general philosophical audience; the statistical parts are pretty informal. *Happy birthday Peirce*.

**Peircean Induction and the Error-Correcting Thesis**

Deborah G. Mayo

*Transactions of the Charles S. Peirce Society: A Quarterly Journal in American Philosophy*, Volume 41, Number 2, 2005, pp. 299-319

Peirce’s philosophy of inductive inference in science is based on the idea that what permits us to make progress in science, what allows our knowledge to grow, is the fact that science uses methods that are self-correcting or error-correcting:

Induction is the experimental testing of a theory. The justification of it is that, although the conclusion at any stage of the investigation may be more or less erroneous, yet the further application of the same method must correct the error. (5.145)

## (Part 3) Peircean Induction and the Error-Correcting Thesis

**Last third of “Peircean Induction and the Error-Correcting Thesis”**

Deborah G. Mayo

*Transactions of the Charles S. Peirce Society *41(2) 2005: 299-319

Part 2 is here.

**8. Random sampling and the uniformity of nature**

We are now at the point to address the final move in warranting Peirce’s SCT. The severity or trustworthiness assessment, on which the error correcting capacity depends, requires an appropriate link (qualitative or quantitative) between the data and the data generating phenomenon, e.g., a reliable calibration of a scale in a qualitative case, or a probabilistic connection between the data and the population in a quantitative case. Establishing such a link, however, is regarded as assuming observed regularities will persist, or making some “uniformity of nature” assumption—the bugbear of attempts to justify induction.

But Peirce contrasts his position with those favored by followers of Mill, and “almost all logicians” of his day, who “commonly teach that the inductive conclusion approximates to the truth because of the uniformity of nature” (2.775). Inductive inference, as Peirce conceives it (i.e., severe testing) does not use the uniformity of nature as a premise. Rather, the justification is sought in the manner of obtaining data. Justifying induction is a matter of showing that there exist methods with good error probabilities. For this it suffices that randomness be met only approximately, that inductive methods check their own assumptions, and that they can often detect and correct departures from randomness.

… It has been objected that the sampling cannot be random in this sense. But this is an idea which flies far away from the plain facts. Thirty throws of a die constitute an approximately random sample of all the throws of that die; and that the randomness should be approximate is all that is required. (1.94)

## (Part 2) Peircean Induction and the Error-Correcting Thesis

**Continuation of “Peircean Induction and the Error-Correcting Thesis”**

Deborah G. Mayo

*Transactions of the Charles S. Peirce Society: A Quarterly Journal in American Philosophy*, Volume 41, Number 2, 2005, pp. 299-319

Part 1 is here.

There are two other points of confusion in critical discussions of the SCT, that we may note here:

*I. The SCT and the Requirements of Randomization and Predesignation*

The concern with “the trustworthiness of the proceeding” for Peirce like the concern with error probabilities (e.g., significance levels) for error statisticians generally, is directly tied to their view that inductive method should closely link inferences to the methods of data collection as well as to how the hypothesis came to be formulated or chosen for testing.

This account of the rationale of induction is distinguished from others in that it has as its consequences two rules of inductive inference which are very frequently violated (1.95) namely, that the sample be (approximately) random and that the property being tested not be determined by the particular sample ** x**— i.e., predesignation.

The picture of Peircean induction that one finds in critics of the SCT disregards these crucial requirements for induction: Neither enumerative induction nor H-D testing, as ordinarily conceived, requires such rules. Statistical significance testing, however, clearly does. Continue reading

## Peircean Induction and the Error-Correcting Thesis (Part I)

Yesterday was C.S. Peirce’s birthday. He’s one of my all time heroes. You should read him: he’s a treasure chest on essentially any topic. I only recently discovered a passage where Popper calls Peirce one of the greatest philosophical thinkers ever (I don’t have it handy). If Popper had taken a few more pages from Peirce, he would have seen how to solve many of the problems in his work on scientific inference, probability, and severe testing. I’ll blog the main sections of a (2005) paper of mine over the next few days. It’s written for a very general philosophical audience; the statistical parts are pretty informal. I first posted it in 2013. *Happy **(slightly belated)** Birthday Peirce*.

**Peircean Induction and the Error-Correcting Thesis**

Deborah G. Mayo

*Transactions of the Charles S. Peirce Society: A Quarterly Journal in American Philosophy*, Volume 41, Number 2, 2005, pp. 299-319

Peirce’s philosophy of inductive inference in science is based on the idea that what permits us to make progress in science, what allows our knowledge to grow, is the fact that science uses methods that are self-correcting or error-correcting:

Induction is the experimental testing of a theory. The justification of it is that, although the conclusion at any stage of the investigation may be more or less erroneous, yet the further application of the same method must correct the error. (5.145)

Inductive methods—understood as methods of experimental testing—are justified to the extent that they are error-correcting methods. We may call this Peirce’s error-correcting or self-correcting thesis (SCT):

**Self-Correcting Thesis SCT:** methods for inductive inference in science are error correcting; the justification for inductive methods of experimental testing in science is that they are self-correcting. Continue reading

## “The Supernal Powers Withhold Their Hands And Let Me Alone” : C.S. Peirce

**Memory Lane* in Honor of C.S. Peirce’s Birthday:
(Part 3) of “Peircean Induction and the Error-Correcting Thesis”**

Deborah G. Mayo

*Transactions of the Charles S. Peirce Society *41(2) 2005: 299-319

(9/10) Peircean Induction and the Error-Correcting Thesis (Part I)

(9/10) (Part 2) Peircean Induction and the Error-Correcting Thesis

**8. Random sampling and the uniformity of nature**

We are now at the point to address the final move in warranting Peirce’s [self-correcting thesis] SCT. The severity or trustworthiness assessment, on which the error correcting capacity depends, requires an appropriate link (qualitative or quantitative) between the data and the data generating phenomenon, e.g., a reliable calibration of a scale in a qualitative case, or a probabilistic connection between the data and the population in a quantitative case. Establishing such a link, however, is regarded as assuming observed regularities will persist, or making some “uniformity of nature” assumption—the bugbear of attempts to justify induction.

But Peirce contrasts his position with those favored by followers of Mill, and “almost all logicians” of his day, who “commonly teach that the inductive conclusion approximates to the truth because of the uniformity of nature” (2.775). Inductive inference, as Peirce conceives it (i.e., severe testing) does not use the uniformity of nature as a premise. Rather, the justification is sought in the manner of obtaining data. Justifying induction is a matter of showing that there exist methods with good error probabilities. For this it suffices that randomness be met only approximately, that inductive methods check their own assumptions, and that they can often detect and correct departures from randomness.

… It has been objected that the sampling cannot be random in this sense. But this is an idea which flies far away from the plain facts. Thirty throws of a die constitute an approximately random sample of all the throws of that die; and that the randomness should be approximate is all that is required. (1.94)

Peirce backs up his defense with robustness arguments. For example, in an (attempted) Binomial induction, Peirce asks, “what will be the effect upon inductive inference of an imperfection in the strictly random character of the sampling” (2.728). What if, for example, a certain proportion of the population had twice the probability of being selected? He shows that “an imperfection of that kind in the random character of the sampling will only weaken the inductive conclusion, and render the concluded ratio less determinate, but will not necessarily destroy the force of the argument completely” (2.728). This is particularly so if the sample mean is near 0 or 1. In other words, violating experimental assumptions may be shown to weaken the trustworthiness or severity of the proceeding, but this may only mean we learn a little less.

Yet a further safeguard is at hand:

Nor must we lose sight of the constant tendency of the inductive process to correct itself. This is of its essence. This is the marvel of it. …even though doubts may be entertained whether one selection of instances is a random one, yet a different selection, made by a different method, will be likely to vary from the normal in a different way, and if the ratios derived from such different selections are nearly equal, they may be presumed to be near the truth. (2.729)

Here, the marvel is an inductive method’s ability to correct the attempt at random sampling. Still, Peirce cautions, we should not depend so much on the self-correcting virtue that we relax our efforts to get a random and independent sample. But if our effort is not successful, and neither is our method robust, we will probably discover it. “This consideration makes it extremely advantageous in all ampliative reasoning to fortify one method of investigation by another” (ibid.). Continue reading

## (Part 3) Peircean Induction and the Error-Correcting Thesis

**Last third of “Peircean Induction and the Error-Correcting Thesis”**

Deborah G. Mayo

*Transactions of the Charles S. Peirce Society *41(2) 2005: 299-319

Part 2 is here.

**8. Random sampling and the uniformity of nature**

We are now at the point to address the final move in warranting Peirce’s SCT. The severity or trustworthiness assessment, on which the error correcting capacity depends, requires an appropriate link (qualitative or quantitative) between the data and the data generating phenomenon, e.g., a reliable calibration of a scale in a qualitative case, or a probabilistic connection between the data and the population in a quantitative case. Establishing such a link, however, is regarded as assuming observed regularities will persist, or making some “uniformity of nature” assumption—the bugbear of attempts to justify induction.

But Peirce contrasts his position with those favored by followers of Mill, and “almost all logicians” of his day, who “commonly teach that the inductive conclusion approximates to the truth because of the uniformity of nature” (2.775). Inductive inference, as Peirce conceives it (i.e., severe testing) does not use the uniformity of nature as a premise. Rather, the justification is sought in the manner of obtaining data. Justifying induction is a matter of showing that there exist methods with good error probabilities. For this it suffices that randomness be met only approximately, that inductive methods check their own assumptions, and that they can often detect and correct departures from randomness.

… It has been objected that the sampling cannot be random in this sense. But this is an idea which flies far away from the plain facts. Thirty throws of a die constitute an approximately random sample of all the throws of that die; and that the randomness should be approximate is all that is required. (1.94)

Peirce backs up his defense with robustness arguments. For example, in an (attempted) Binomial induction, Peirce asks, “what will be the effect upon inductive inference of an imperfection in the strictly random character of the sampling” (2.728). What if, for example, a certain proportion of the population had twice the probability of being selected? He shows that “an imperfection of that kind in the random character of the sampling will only weaken the inductive conclusion, and render the concluded ratio less determinate, but will not necessarily destroy the force of the argument completely” (2.728). This is particularly so if the sample mean is near 0 or 1. In other words, violating experimental assumptions may be shown to weaken the trustworthiness or severity of the proceeding, but this may only mean we learn a little less.

Yet a further safeguard is at hand:

Nor must we lose sight of the constant tendency of the inductive process to correct itself. This is of its essence. This is the marvel of it. …even though doubts may be entertained whether one selection of instances is a random one, yet a different selection, made by a different method, will be likely to vary from the normal in a different way, and if the ratios derived from such different selections are nearly equal, they may be presumed to be near the truth. (2.729)

Here, the marvel is an inductive method’s ability to correct the attempt at random sampling. Still, Peirce cautions, we should not depend so much on the self-correcting virtue that we relax our efforts to get a random and independent sample. But if our effort is not successful, and neither is our method robust, we will probably discover it. “This consideration makes it extremely advantageous in all ampliative reasoning to fortify one method of investigation by another” (ibid.).

*“The Supernal Powers Withhold Their Hands And Let Me Alone”*

Peirce turns the tables on those skeptical about satisfying random sampling—or, more generally, satisfying the assumptions of a statistical model. He declares himself “willing to concede, in order to concede as much as possible, that when a man draws instances at random, all that he knows is that he tried to follow a certain precept” (2.749). There might be a “mysterious and malign connection between the mind and the universe” that deliberately thwarts such efforts. He considers betting on the game of *rouge et noire*: “could some devil look at each card before it was turned, and then influence me mentally” to bet or not, the ratio of successful bets might differ greatly from 0.5. But, as Peirce is quick to point out, this would equally vitiate deductive inferences about the expected ratio of successful bets.

Consider our informal example of weighing with calibrated scales. If I check the properties of the scales against known, standard weights, then I can check if my scales are working in a particular case. Were the scales infected by systematic error, I would discover this by finding systematic mismatches with the known weights; I could then subtract it out in measurements. That scales have given properties where I know the object’s weight indicates they have the same properties when the weights are unknown, lest I be forced to assume that my knowledge or ignorance somehow influences the properties of the scale. More generally, Peirce’s insightful argument goes, the experimental procedure thus confirmed where the measured property is known must work as well when it is unknown unless a mysterious and malign demon deliberately thwarts my efforts. Continue reading

## (Part 2) Peircean Induction and the Error-Correcting Thesis

**Continuation of “Peircean Induction and the Error-Correcting Thesis”**

Deborah G. Mayo

*Transactions of the Charles S. Peirce Society: A Quarterly Journal in American Philosophy*, Volume 41, Number 2, 2005, pp. 299-319

Part 1 is here.

There are two other points of confusion in critical discussions of the SCT, that we may note here:

*I. The SCT and the Requirements of Randomization and Predesignation*

The concern with “the trustworthiness of the proceeding” for Peirce like the concern with error probabilities (e.g., significance levels) for error statisticians generally, is directly tied to their view that inductive method should closely link inferences to the methods of data collection as well as to how the hypothesis came to be formulated or chosen for testing.

This account of the rationale of induction is distinguished from others in that it has as its consequences two rules of inductive inference which are very frequently violated (1.95) namely, that the sample be (approximately) random and that the property being tested not be determined by the particular sample ** x**— i.e., predesignation.

The picture of Peircean induction that one finds in critics of the SCT disregards these crucial requirements for induction: Neither enumerative induction nor H-D testing, as ordinarily conceived, requires such rules. Statistical significance testing, however, clearly does.

Suppose, for example that researchers wishing to demonstrate the benefits of HRT search the data for factors on which treated women fare much better than untreated, and finding one such factor they proceed to test the null hypothesis:

*H _{0}*: there is no improvement in factor F (e.g. memory) among women treated with HRT.

Having selected this factor for testing solely because it is a factor on which treated women show impressive improvement, it is not surprising that this null hypothesis is rejected and the results taken to show a genuine improvement in the population. However, when the null hypothesis is tested on the same data that led it to be chosen for testing, it is well known, a spurious impression of a genuine effect easily results. Suppose, for example, that 20 factors are examined for impressive-looking improvements among HRT-treated women, and the one difference that appears large enough to test turns out to be significant at the 0.05 level. The actual significance level—the actual probability of reporting a statistically significant effect when in fact the null hypothesis is true—is not 5% but approximately 64% (Mayo 1996, Mayo and Kruse 2001, Mayo and Cox 2006). To infer the denial of *H _{0}*, and infer there is evidence that HRT improves memory, is to make an inference with low severity (approximately 0.36).

*II Understanding the “long-run error correcting” metaphor*

Discussions of Peircean ‘self-correction’ often confuse two interpretations of the ‘long-run’ error correcting metaphor, even in the case of quantitative induction: *(a) Asymptotic self-correction (as **n* approaches ∞): In this construal, it is imagined that one has a sample, say of size *n*=10, and it is supposed that the SCT assures us that as the sample size increases toward infinity, one gets better and better estimates of some feature of the population, say the mean. Although this may be true, provided assumptions of a statistical model (e.g., the Binomial) are met, it is not the sense intended in significance-test reasoning nor, I maintain, in Peirce’s SCT. Peirce’s idea, instead, gives needed insight for understanding the relevance of ‘long-run’ error probabilities of significance tests to assess the reliability of an inductive inference from a specific set of data, *(b) Error probabilities of a test:* In this construal, one has a sample of size *n*, say 10, and imagines hypothetical replications of the experiment—each with samples of 10. Each sample of 10 gives a single value of the test statistic ** d(X)**, but one can consider the distribution of values that would occur in hypothetical repetitions (of the given type of sampling). The probability distribution of

**is called the sampling distribution, and the correct calculation of the significance level is an example of how tests appeal to this distribution: Thanks to the relationship between the observed**

*d(X)***and the sampling distribution of**

*d(x)***, the former can be used to reliably probe the correctness of statistical hypotheses (about the procedure) that generated the particular 10-fold sample. That is what the SCT is asserting.**

*d(X)*It may help to consider a very informal example. Suppose that weight gain is measured by 10 well-calibrated and stable methods, possibly using several measuring instruments and the results show negligible change over a test period of interest. This may be regarded as grounds for inferring that the individual’s weight gain is negligible within limits set by the sensitivity of the scales. Why? While it is true that by averaging more and more weight measurements, i.e., an eleventh, twelfth, etc., one would get asymptotically close to the true weight, that is not the rationale for the particular inference. The rationale is rather that the error probabilistic properties of the weighing procedure (the probability of ten-fold weighings erroneously failing to show weight change) inform one of the correct weight in the case at hand, e.g., that a 0 observed weight increase passes the “no-weight gain” hypothesis with high severity. Continue reading

## Peircean Induction and the Error-Correcting Thesis (Part I)

Today is C.S. Peirce’s birthday. I hadn’t blogged him before, but he’s one of my all time heroes. You should read him: he’s a treasure chest on essentially any topic. I’ll blog the main sections of a (2005) paper over the next few days. It’s written for a very general philosophical audience; the statistical parts are pretty informal. *Happy birthday Peirce*.

**Peircean Induction and the Error-Correcting Thesis**

Deborah G. Mayo

*Transactions of the Charles S. Peirce Society: A Quarterly Journal in American Philosophy*, Volume 41, Number 2, 2005, pp. 299-319

Peirce’s philosophy of inductive inference in science is based on the idea that what permits us to make progress in science, what allows our knowledge to grow, is the fact that science uses methods that are self-correcting or error-correcting:

Induction is the experimental testing of a theory. The justification of it is that, although the conclusion at any stage of the investigation may be more or less erroneous, yet the further application of the same method must correct the error. (5.145)

Inductive methods—understood as methods of experimental testing—are justified to the extent that they are error-correcting methods. We may call this Peirce’s error-correcting or self-correcting thesis (SCT):

**Self-Correcting Thesis SCT:** methods for inductive inference in science are error correcting; the justification for inductive methods of experimental testing in science is that they are self-correcting.

Peirce’s SCT has been a source of fascination and frustration. By and large, critics and followers alike have denied that Peirce can sustain his SCT as a way to justify scientific induction: “No part of Peirce’s philosophy of science has been more severely criticized, even by his most sympathetic commentators, than this attempted validation of inductive methodology on the basis of its purported self-correctiveness” (Rescher 1978, p. 20).

In this paper I shall revisit the Peircean SCT: properly interpreted, I will argue, Peirce’s SCT not only serves its intended purpose, it also provides the basis for justifying (frequentist) statistical methods in science. While on the one hand, contemporary statistical methods increase the mathematical rigor and generality of Peirce’s SCT, on the other, Peirce provides something current statistical methodology lacks: an account of inductive inference and a philosophy of experiment that links the justification for statistical tests to a more general rationale for scientific induction. Combining the mathematical contributions of modern statistics with the inductive philosophy of Peirce, sets the stage for developing an adequate justification for contemporary inductive statistical methodology.

**2. Probabilities are assigned to procedures not hypotheses**

Peirce’s philosophy of experimental testing shares a number of key features with the contemporary (Neyman and Pearson) Statistical Theory: statistical methods provide, not means for assigning degrees of probability, evidential support, or confirmation to hypotheses, but procedures for testing (and estimation), whose rationale is their predesignated high frequencies of leading to correct results in some hypothetical long-run. A Neyman and Pearson (NP) statistical test, for example, instructs us “To decide whether a hypothesis, *H*, of a given type be rejected or not, calculate a specified character, ** x_{0}**, of the observed facts; if

**>**

*x***reject**

*x*_{0 }*H*; if

**<**

*x***accept**

*x*_{0}*H*.” Although the outputs of N-P tests do not assign hypotheses degrees of probability, “it may often be proved that if we behave according to such a rule … we shall reject

*H*when it is true not more, say, than once in a hundred times, and in addition we may have evidence that we shall reject

*H*sufficiently often when it is false” (Neyman and Pearson, 1933, p.142).[i]

The relative frequencies of erroneous rejections and erroneous acceptances in an actual or hypothetical long run sequence of applications of tests are error probabilities; we may call the statistical tools based on error probabilities, error statistical tools. In describing his theory of inference, Peirce could be describing that of the error-statistician:

The theory here proposed does not assign any probability to the inductive or hypothetic conclusion, in the sense of undertaking to say how frequently that conclusion would be found true. It does not propose to look through all the possible universes, and say in what proportion of them a certain uniformity occurs; such a proceeding, were it possible, would be quite idle. The theory here presented only says how frequently, in this universe, the special form of induction or hypothesis would lead us right. The probability given by this theory is in every way different—in meaning, numerical value, and form—from that of those who would apply to ampliative inference the doctrine of inverse chances. (2.748)

The doctrine of “inverse chances” alludes to assigning (posterior) probabilities in hypotheses by applying the definition of conditional probability (Bayes’s theorem)—a computation requires starting out with a (prior or “antecedent”) probability assignment to an exhaustive set of hypotheses:

If these antecedent probabilities were solid statistical facts, like those upon which the insurance business rests, the ordinary precepts and practice [of inverse probability] would be sound. But they are not and cannot be statistical facts. What is the antecedent probability that matter should be composed of atoms? Can we take statistics of a multitude of different universes? (2.777)

For Peircean induction, as in the N-P testing model, the conclusion or inference concerns a hypothesis that either is or is not true in this one universe; thus, assigning a frequentist probability to a particular conclusion, other than the trivial ones of 1 or 0, for Peirce, makes sense only “if universes were as plentiful as blackberries” (2.684). Thus the Bayesian inverse probability calculation seems forced to rely on subjective probabilities for computing inverse inferences, but “subjective probabilities” Peirce charges “express nothing but the conformity of a new suggestion to our prepossessions, and these are the source of most of the errors into which man falls, and of all the worse of them” (2.777).

Hearing Pierce contrast his view of induction with the more popular Bayesian account of his day (the Conceptualists), one could be listening to an error statistician arguing against the contemporary Bayesian (subjective or other)—with one important difference. Today’s error statistician seems to grant too readily that the only justification for N-P test rules is their ability to ensure we will rarely take erroneous actions with respect to hypotheses in the long run of applications. This so called inductive behavior rationale seems to supply no adequate answer to the question of what is learned in any particular application about the process underlying the data. Peirce, by contrast, was very clear that what is really wanted in inductive inference in science is the ability to control error probabilities of test procedures, i.e., “the trustworthiness of the proceeding”. Moreover it is only by a faulty analogy with deductive inference, Peirce explains, that many suppose that inductive (synthetic) inference should supply a probability to the conclusion: “… in the case of analytic inference we know the probability of our conclusion (if the premises are true), but in the case of synthetic inferences we only know the degree of trustworthiness of our proceeding (“The Probability of Induction” 2.693).

Knowing the “trustworthiness of our inductive proceeding”, I will argue, enables determining the test’s probative capacity, how reliably it detects errors, and the severity of the test a hypothesis withstands. Deliberately making use of known flaws and fallacies in reasoning with limited and uncertain data, tests may be constructed that are highly trustworthy probes in detecting and discriminating errors in particular cases. This, in turn, enables inferring which inferences about the process giving rise to the data are and are not warranted: an inductive inference to hypothesis *H* is warranted to the extent that with high probability the test would have detected a specific flaw or departure from what *H* asserts, and yet it did not.

**3. So why is justifying Peirce’s SCT thought to be so problematic?**

You can read Section 3 here. (it’s not necessary for understanding the rest).

**4. Peircean induction as severe testing**

… [I]nduction, for Peirce, is a matter of subjecting hypotheses to “the test of experiment” (7.182).

The process of testing it will consist, not in examining the facts, in order to see how well they accord with the hypothesis, but on the contrary in examining such of the probable consequences of the hypothesis … which would be very unlikely or surprising in case the hypothesis were not true. (7.231)

When, however, we find that prediction after prediction, notwithstanding a preference for putting the most unlikely ones to the test, is verified by experiment,…we begin to accord to the hypothesis a standing among scientific results.

This sort of inference it is, from experiments testing predictions based on a hypothesis, that is alone properly entitled to be called induction. (7.206)

While these and other passages are redolent of Popper, Peirce differs from Popper in crucial ways. Peirce, unlike Popper, is primarily interested not in falsifying claims but in the positive pieces of information provided by tests, with “the corrections called for by the experiment” and with the hypotheses, modified or not, that manage to pass severe tests. For Popper, even if a hypothesis is highly *corroborated (by his lights)*, he regards this as at most a report of the hypothesis’ past performance and denies it affords positive evidence for its correctness or reliability. Further, Popper denies that he could vouch for the reliability of the method he recommends as “most rational”—conjecture and refutation. Indeed, Popper’s requirements for a highly corroborated hypothesis are not sufficient for ensuring severity in Peirce’s sense (Mayo 1996, 2003, 2005). Where Popper recoils from even speaking of warranted inductions, Peirce conceives of a proper inductive inference as what had passed a severe test—one which would, with high probability, have detected an error if present.

In Peirce’s inductive philosophy, we have evidence for inductively inferring a claim or hypothesis *H* when not only does *H* “accord with” the data ** x**; but also, so good an accordance would very probably not have resulted, were

*H*not true. In other words, we may inductively infer

*H*when it has withstood a test of experiment that it would not have withstood, or withstood so well, were H not true (or were a specific flaw present). This can be encapsulated in the following severity requirement for an experimental test procedure, ET, and data set

**.**

*x**Hypothesis H passes a severe test with* ** x** iff (firstly)

**accords with**

*x**H*and (secondly) the experimental test procedure ET would, with very high probability, have signaled the presence of an error were there a discordancy between what

*H*asserts and what is correct (i.e., were

*H*false).

The test would “have signaled an error” by having produced results less accordant with *H* than what the test yielded. Thus, we may inductively infer *H* when (and only when) *H* has withstood a test with high error detecting capacity, the higher this probative capacity, the more severely *H* has passed. What is assessed (quantitatively or qualitatively) is not the amount of support for *H* but the probative capacity of the test of experiment ET (with regard to those errors that an inference to *H* is declaring to be absent)……….

You can read the rest of Section 4 here here

**5. The path from qualitative to quantitative induction**

In my understanding of Peircean induction, the difference between qualitative and quantitative induction is really a matter of degree, according to whether their trustworthiness or severity is quantitatively or only qualitatively ascertainable. This reading not only neatly organizes Peirce’s typologies of the various types of induction, it underwrites the manner in which, within a given classification, Peirce further subdivides inductions by their “strength”.

*(I) First-Order, Rudimentary or Crude Induction*

Consider Peirce’s First Order of induction: the lowest, most rudimentary form that he dubs, the “pooh-pooh argument”. It is essentially an argument from ignorance: Lacking evidence for the falsity of some hypothesis or claim *H*, provisionally adopt *H*. In this very weakest sort of induction, crude induction, the most that can be said is that a hypothesis would eventually be falsified if false. (It may correct itself—but with a bang!) It “is as weak an inference as any that I would not positively condemn” (8.237). While uneliminable in ordinary life, Peirce denies that rudimentary induction is to be included as scientific induction. Without some reason to think evidence of *H*‘s falsity would probably have been detected, were H false, finding no evidence against *H* is poor inductive evidence *for* *H*. *H* has passed only a highly unreliable error probe. Continue reading