Hume’s Problem of Induction

Most of our beliefs about the world have been formed from inductive inference. (e.g., all of science, folk physics/psych) Hume’s Problem of Induction Hume concludes that we have no reason at all to think these beliefs are true.

Hume’s Problem of Induction Epistemology: the study of knowledge and the justification of belief. A central sub-field in philosophy The problem of induction is a classic epistemological issue.

Plato (~2,500 years ago) : Knowledge = justified true belief To have knowledge: 1)A person must believe a proposition. 2)She must believe it for good reasons. 3)The proposition must be true.

Plato (~2,500 years ago) : Knowledge = justified true belief To have knowledge: 1)A person must believe a proposition. 2)She must believe it for good reasons. 3)The proposition must be true. Even if a belief is true, someone may hold it for the wrong reasons. Accidentally true beliefs aren’t knowledge.

Imagine seeing this in a tabloid: Brad and Angelina Adopt Three-headed Baby! Would you be justified in believing this just on the basis of a tabloid headline?

Imagine seeing this in a tabloid: Brad and Angelina Adopt Three-headed Baby! Even if it’s true, as long as your only reason for believing this is that you saw it in a tabloid, you don’t really know that Brad and Angelina have a three-headed baby. Your belief is based on bad reasons. You may have true belief but still lack justification.

This is the sort of objection Hume makes against induction:

This is the sort of objection Hume makes against induction: Inductive beliefs aren’t justified. They could be true, but we have no reason to think so. If they happen to be true, it’s just an accident.

The point is not that inductive beliefs are false, but that we can’t tell whether they’re false or not. If they happen to be false, we won’t know it. If they happen to be true, it’s just an accident.

According to Hume, We might as well get our scientific beliefs out of the tabloids.

Recall the difference: 1)Evaluating an argument 2)Evaluating a conclusion Hume’s point is that the arguments supporting induction all fail. He considers 3: - 2 deductive -1 inductive

A severe form of skepticism Others have been skeptical of knowledge, rather than justification:

A severe form of skepticism Others have been skeptical of knowledge, rather than justification: Descartes notes that knowledge requires certainty... If you aren’t really sure about something, you can’t say you know. You just believe.

A severe form of skepticism Others have been skeptical of knowledge, rather than justification: Descartes notes that knowledge requires certainty... If you aren’t really sure about something, you can’t say you know. You just believe....then he shows that we aren’t certain about much. So we don’t know much.

A severe form of skepticism Still, even if you don’t really know something, you can be justified in believing it. Beliefs can at least be rational, even if you aren’t certain about them.

A severe form of skepticism Still, even if you don’t really know something, you can be justified in believing it. Beliefs can at least be rational, even if you aren’t certain about them. Hume says you can’t even say this much in favor of induction: It’s irrational to believe things for no good reason.

1)Induction is justified only if PUN is justified. 2)PUN can be justified only by induction or by deduction. 3)PUN can’t be justified by induction. 4)PUN can’t be justified by deduction. PUN can’t be justified at all. Induction isn’t justified. (PUN = Principle of Uniformity of Nature) Hume’s Basic Argument:

What’s PUN? Uniformity between past and future Predictions of the future are based on patterns observed in the past. They assume that the patterns we’ve observed in the past will continue into the future.

What’s PUN? Patterns: A reliably comes before B. FireSmoke Lightning Thunder AB Sunshine Sunburn

1)In the past, lightning has reliably preceded thunder. In the future, lightning will continue to precede thunder. 2) PUN: patterns from the past will continue in the future. What’s PUN?

1)In the past, sunburns have reliably appeared after sun exposure. In the future, sunburns will continue to appear after sun exposure. 2) PUN: patterns from the past will continue in the future.

What’s PUN? FireSmoke PastFuture AB SunBurn FireSmoke AB SunBurn =

1)Induction is justified only if PUN is justified. 2)PUN can be justified only by induction or by deduction. 3)PUN can’t be justified by induction. 4)PUN can’t be justified by deduction. PUN can’t be justified at all. Induction isn’t justified. Hume’s Basic Argument:

1)Induction is justified only if PUN is justified. Hume’s Basic Argument:

1)Induction is justified only if PUN is justified. Hume’s Basic Argument: 1)In the past, lightning has reliably come before thunder. In the future, lightning will come before thunder. Consider this inference: How do we make this connection?

1)Induction is justified only if PUN is justified. Hume’s Basic Argument: 1)In the past, lightning has reliably come before thunder. In the future, lightning will come before thunder. Does this follow logically?

1)Induction is justified only if PUN is justified. Hume’s Basic Argument: 1)In the past, lightning has reliably come before thunder. In the future, lightning will come before thunder. Does this follow logically? No.

1)Induction is justified only if PUN is justified. Hume’s Basic Argument: 1)In the past, lightning has reliably come before thunder. In the future, lightning will come before thunder. 2) PUN: patterns from the past will continue in the future.

1)Induction is justified only if PUN is justified. Hume’s Basic Argument: 1)In the past, the sun has risen every morning. In the future, the sun will rise every morning. Without PUN, there’s no connection between observation and prediction. Observation Prediction 2) PUN: patterns from the past will continue in the future.

1)Induction is justified only if PUN is justified. 2)PUN can be justified only by induction or by deduction. 3)PUN can’t be justified by induction. 4)PUN can’t be justified by deduction. PUN can’t be justified at all. Induction isn’t justified. Hume’s Basic Argument:

1)Induction is justified only if PUN is justified. 2)PUN can be justified only by induction or by deduction. Hume’s Basic Argument: Hume wrote before abduction was “discovered,” so induction and deduction were all he knew about. But would it matter? Could PUN be needed as the best explanation for something?

Can PUN be justified by abduction? Can you think of any observations that we might need PUN to explain? ??? HYP: OBS: Discuss in groups: PUN: patterns from the past will continue in the future.

??? HYP: OBS: Past How could events that haven’t happened yet be the explanation for events that have already happened? PUN: patterns from the past will continue in the future. PUN is a claim about what’s going to happen in the future. But to justify PUN by abduction we’d need to show that it’s the best explanation for something we’ve already observed.

1)Induction is justified only if PUN is justified. 2)PUN can be justified only by induction or by deduction. 3)PUN can’t be justified by induction. 4)PUN can’t be justified by deduction. PUN can’t be justified at all. Induction isn’t justified. Hume’s Basic Argument:

3) PUN can’t be justified by induction. A natural thought is that the success of induction supports the truth of PUN: We constantly make predictions based on observed patterns, and most of them turn out to be accurate. The best explanation for this success is that patterns do continue into the future.

3) PUN can’t be justified by induction. But look closely: We constantly make predictions based on observed patterns, and most of them turn out to be accurate. The best explanation for this success is that patterns do continue into the future. did have made turned out Observed cases of successful prediction have all occurred in the past.

3) PUN can’t be justified by induction. But look closely: We constantly make predictions based on observed patterns, and most of them turn out to be accurate. The best explanation for this success is that patterns do continue into the future. did have made turned out This shows only that nature was uniform, back when the predictions were tested.

1)In the past, the sun has risen every morning. In the future, the sun will rise every morning. 1)In the past, patterns from the past continued into the future. In the future, patterns from the past will continue into the future.

1)In the past, the sun has risen every morning. In the future, the sun will rise every morning. 1)In the past, patterns from the past continued into the future. In the future, patterns from the past will continue into the future. 2) PUN: patterns from the past will continue in the future.

1)In the past, the sun has risen every morning. In the future, the sun will rise every morning. 1)In the past, patterns from the past continued into the future. In the future, patterns from the past will continue into the future. 2) PUN: patterns from the past will continue in the future.

1)In the past, the sun has risen every morning. In the future, the sun will rise every morning. 1)In the past, patterns from the past continued into the future. In the future, patterns from the past will continue into the future. 2) PUN: patterns from the past will continue in the future.

1)In the past, patterns from the past continued into the future. In the future, patterns from the past will continue into the future. 2) PUN: patterns from the past will continue in the future. The argument is circular. Induction only works if PUN is already true (Premise 1), so any attempt to justify PUN using an inductive argument will have to assume its own conclusion in the premises.

1)Induction is justified only if PUN is justified. 2)PUN can be justified only by induction or by deduction. 3)PUN can’t be justified by induction. 4)PUN can’t be justified by deduction. PUN can’t be justified at all. Induction isn’t justified. Hume’s Basic Argument:

4) PUN can’t be justified by deduction.

Hume considers two ways that PUN might be justified by deduction: 1)If we could deduce the uniformity of nature directly from what we observe. 2)If it followed somehow from the meaning of PUN that nature was uniform. Neither approach works. 4) PUN can’t be justified by deduction.

1)Could we deduce uniformity directly from what we observe? This would mean that facts about the future follow logically from what we’ve observed the past. 4) PUN can’t be justified by deduction.

1)Could we deduce uniformity directly from what we observe? This would mean that facts about the future follow logically from what we’ve observed the past. 4) PUN can’t be justified by deduction. But we’ve already considered this...

1)Could we deduce uniformity directly from what we observe? 4) PUN can’t be justified by deduction. 1)In the past, the sun has risen every morning. In the future, the sun will rise every morning. Does this follow logically?

1)Could we deduce uniformity directly from what we observe? 4) PUN can’t be justified by deduction. No. 1)In the past, the sun has risen every morning. In the future, the sun will rise every morning. Does this follow logically?

1)In the past, the sun has risen every morning. In the future, the sun will rise every morning. Without PUN, there’s no connection between observation and prediction. Observation Prediction 1)Could we deduce uniformity directly from what we observe? 4) PUN can’t be justified by deduction.

1)In the past, the sun has risen every morning. In the future, the sun will rise every morning. Without PUN, there’s no connection between observation and prediction. Observation Prediction 1)Could we deduce uniformity directly from what we observe? 4) PUN can’t be justified by deduction. 2) PUN: patterns from the past will continue in the future.

2) Does the uniformity of nature follow by definition, from the meaning of PUN? 4) PUN can’t be justified by deduction. Definitional truths: There’s no such thing as a 5-sided triangle. Salted butter contains salt. These claims are true in virtue of what it means to be a triangle, or to be salted.

The same applies, Hume notes, for the uniformity principle. The idea of a 5-sided triangle, or of salted butter containing no salt, would be a contradiction—incoherent and impossible to imagine. 2) Does the uniformity of nature follow by definition, from the meaning of PUN? 4) PUN can’t be justified by deduction.

It isn’t. We can easily imagine the sun not rising. If it were a definitional truth that the future resembles the past, then the idea of patterns not continuing into the future would be like the idea of a 5-sided triangle: incoherent and impossible to even imagine. 2) Does the uniformity of nature follow by definition, from the meaning of PUN? 4) PUN can’t be justified by deduction.

1)Induction is justified only if PUN is justified. 2)PUN can be justified only by induction or by deduction. 3)PUN can’t be justified by induction. 4)PUN can’t be justified by deduction. PUN can’t be justified at all. Induction isn’t justified. Hume’s Basic Argument:

In the textbook, Sober says it’s hard to specify exactly what PUN means. The future will resemble the past in certain respects, but not in all respects. How do we say in general what it is about the future that resembles the past? For this reason, Sober replaces Hume’s argument with a different one based on reliability, rather than PUN.

In the textbook, Sober says it’s hard to specify exactly what PUN means. The future will resemble the past in certain respects, but not in all respects. How do we say in general what it is about the future that resembles the past? For this reason, Sober replaces Hume’s argument with a different one based on reliability, rather than PUN. I’m glossing over this...

I’ve simply defined PUN in terms of reliability: Patterns: A reliably comes before B. FireSmoke AB Lightning Thunder Sunshine Sunburn

What difference does it make? PUN is supposed to describe the world itself. (Principle of the Uniformity of Nature). The patterns I’ve been talking about are patterns in our representations of the world. There’s a difference between our observations and inferences about the world and the world itself.

As I’ve presented it (in terms of patterns) PUN is actually about how our experience of the future resembles our experience of the past. FireSmoke Lightning Thunder Sunshine Sunburn Representations of precede

Sober reformulates Hume’s argument because it’s hard to specify what uniformity is as an objective feature of nature. It’s easier to understand the reliability of inferences than the uniformity of nature itself. Once we’ve identified a given pattern (in our minds), we can define uniformity as the future resembling the past with regard to that pattern.

Fundamental laws of nature describe patterns that are perfectly reliable (e.g., gravity). Maybe perfect patterns of uniformity really are objective features of nature. But most inductive inferences aren’t based on perfect patterns. Sun exposure doesn’t always cause sunburn.

If so, it’s better to see PUN as a principle describing how we represent the past and the future. You must already have a pattern in mind before you can say how the future resembles the past. The problem of induction is supposed to apply to all inductive inferences, including those based on imperfect patterns.

Strict formulation of PUN: Our experience of patterns in the future will resemble our experience of patterns in the past. The problem of induction is supposed to apply to all inductive inferences, including those based on imperfect patterns. If so, it’s better to see PUN as a principle describing how we represent the past and the future.

The Big Picture Induction is a psychological activity: we identify patterns for use in predicting the future. The 99 Bus usually comes every 5-7 minutes, so if I get to the bus stop at 9:20, I’ll get to class by 10:00. Any two bodies in space attract each other with a force proportional to their masses, so if I let go of my pen, it will fall.

The Big Picture Induction is a psychological activity: we identify patterns for use in predicting the future. The 99 Bus usually comes every 5-7 minutes, so if I get to the bus stop at 9:20, I’ll get to class by 10:00. Any two bodies in space attract each other with a force proportional to their masses, so if I let go of my pen, it will fall. Most of the patterns we use in ordinary life are imperfect, but good enough for practical purposes.

The Big Picture Induction is a psychological activity: we identify patterns for use in predicting the future. The 99 Bus usually comes every 5-7 minutes, so if I get to the bus stop at 9:20, I’ll get to class by 10:00. Any two bodies in space attract each other with a force proportional to their masses, so if I let go of my pen, it will fall. The task of science is to identify perfect patterns, those that have no exceptions at all.

Still, science can’t explain perfect patterns. It can only identify them (as we saw on Monday). Laws of nature are explanatorily basic: Science explains imperfect patterns in terms of perfect patterns, but it can’t explain perfect patterns themselves. The Big Picture

Still, science can’t explain perfect patterns. It can only identify them (as we saw on Monday). Laws of nature are explanatorily basic: Science explains imperfect patterns in terms of perfect patterns, but it can’t explain perfect patterns themselves. So even for perfect patterns, science can only assume that the future will resemble the past. The Big Picture

Still, science can’t explain perfect patterns. It can only identify them (as we saw on Monday). Laws of nature are explanatorily basic: Science explains imperfect patterns in terms of perfect patterns, but it can’t explain perfect patterns themselves. So even for perfect patterns, science can only assume that the future will resemble the past. It cannot justify this assumption. The Big Picture

The uniformity of nature is a global fact. Like the origins of the universe, PUN falls outside the scope of scientific explanation. The Big Picture If the future resembles the past in the ways described by laws of nature, then this is a fact for which we have no scientific explanation.

The uniformity of nature is a global fact. Like the origins of the universe, PUN falls outside the scope of scientific explanation. The Big Picture If the future resembles the past in the ways described by laws of nature, then this is a fact for which we have no explanation. Even for laws of nature, we have no good reason to believe the future will resemble the past.

The Big Picture So all of science is based on an assumption for which we have no justification. (We might as well take our scientific beliefs from the tabloids.)

We saw earlier that Hume’s problem is about the justification of induction: There’s no good reason to think induction provides true beliefs. It’s irrational to hold beliefs that you have no reason to think are true.

We saw earlier that Hume’s problem is about the justification of induction: There’s no good reason to think induction provides true beliefs. It’s irrational to hold beliefs that you have no reason to think are true. Do you agree with this assumption? What if you have false beliefs that are good for you? ✔

It’s irrational to hold beliefs that you have no reason to think are true. Do you agree with this assumption? What if you have false beliefs that are good for you? Depressive Realism: depressed people have more accurate beliefs than healthy people about their ability to control events in the world.