You Know Nothing

David Sanson

2026-10-05

Preliminaries

Agenda

1. Preliminaries
2. Exams
3. Knowledge of the Future

Reminders

• We are discussing “You know nothing”.
• I want to divide things up differently this week:
  • Today: you cannot know about the future
  • Wednesday: you cannot know about the present
• Will return exams at end of class.

Exams

Agenda

1. Preliminaries
2. Exams
3. Knowledge of the Future

Short Answer

5 questions \(\times\) 5 points each.

Some common errors:

• giving all three omnis when asked to define just one: 1/5
• giving two out of three (including the correct one): 3/5
• omniscience is the science of everything: 0/5

Short Answer

• saying that suffering always has a reason; pointless suffering does not: 3/5
• pointless suffering is suffering that is thought to have no reason: 3/5
• narrow definitions of pointless suffering, e.g., undeserved suffering: 3/5
• “pointless suffering is suffering without a point”: 2/5

Short Answer

• basically right but no mention of how to calculate expected utility: 3/5
• basically right but wrong calculation: 3/5
• no mention of probabilities, just benefits: 3/5
• calculation given by numbers/variables unexplained: 2/5

Short Answer

• DNA/Fingerprints account correct but not an actual counterexample: 3/5
• Seriously muddled account: 2/5

Short Answer

• ‘only if’ or ‘if’ instead of ‘if and only if’: 5/5
• “some overlap” instead of “mostly overlap”: 4/5
• muddled statement of account: 3/5
• confusing overlap with matching: 3/5
• correct statement but no counterexample/wrong counterexample: 3/5
• seriously muddled statement of account: 2/5
• “multiple people have the same mind”: 0/5

Essays

I graded essays using letter grades. Here is my rough intuitive scale:

Grade	Assessment
A	Nice clean clear answer.
B	Muddled. Some serious mistakes. But not completely confused
C	Shows some knowledge of topic, but very confused.
D	Barely on topic.
F/0	No answer. Or completely off topic.

Essays

I converted these letter grades into 25 point scores using the following scale:

A+	A	A-	B+	B	B-	C+	C	C-	D+	D	F
25	24	23	22	21	20	19	18	17	16	15	0

Bonus Questions

I appreciated those who answered these. Especially those of you who answered 10—the invitation to share your own thoughts! Pretty much everyone who said anything here got 5 points.

Statistics

• Highest: 101
• Lowest: 41
• Average: 71.33
• Median: 72

That is a low median. There were a lot of lost points on short answer questions. The essay grading scale is slightly skewed because of whole numbers: a C is 18/25 = 72%, instead of 75%.

Statistics

• Above 90: 4
• Between 80 and 90: 3
• Between 70 and 80: 9
• Between 60 and 79: 4
• Between 50 and 60: 4
• Between 40 and 50: 3

Adjustment

As a minimal “curve”, I will, when calculating course grades, add 5 points to your score. This will shift the median up to 77 and the average to 76.33.

Adjustment

• Above 90: 5
• Between 80 and 90: 6
• Between 70 and 80: 8
• Between 60 and 79: 3
• Between 50 and 60: 4
• Between 40 and 50: 1

Knowledge of the Future

Agenda

1. Preliminaries
2. Exams
3. Knowledge of the Future

Reflection Questions

1. The argument that FLP is unjustified turns on the claim that induction and direct observation are the only ways of knowing about the world. Is that true? When a detective solves a crime unlike any crime she’s ever seen before, is she using resources other than induction and direct observation? If so, how might that help with resisting the argument?
2. I say that the argument that you do not know that the sun will rise in the west tonight extends to all of your beliefs about the future. Is that true? Can it be used to undermine the belief that 1+1 will still be equal to 2 tomorrow? If not, why not?
3. Can you think of a way of modifying some of the arguments from this chapter to produce an argument that we can’t know anything about the past? (Or anything about the present not around here?)
4. I argued that no one knows anything about the world. Are my arguments self-defeating? Can they also be used to show that I don’t know that no one knows anything about the world? If so, is that a problem? If not, why not?

Direct Observation

Using your sense organs to obtain information that is immediately available to you about your surrounding environment.

What are some things you know by DO? Some things you know, but not by DO?

Induction

Induction is when you reason from a regularity in what you have directly observed to a conclusion about things that you have not directly observed.

Induction

Argument

1. Everything is wet (direct observation)
2. In the past, I’ve directly observed that this happens after it rains.
3. So, it was raining. (not directly observed)

How do you know (2)?

Not foolproof—things could be wet for some other reason. But, as we ordinarily think of things, reasonable.

Induction

Argument

1. In the past, the sun has always set in the west (direct observation)
2. So, the sun will set in the west tonight. (not directly observed)

Is this a good inference? Can we improve it by appeal to astronomy?

FLP

Future Like Past (FLP)

Future states of the world will be like past states of the world.

If you didn’t believe something like FLP, then you wouldn’t think that facts about your past observations gave you any evidence for claims about the future.

Induction—at least, future-oriented induction—seems to presuppose FLP.

Against Knowing the Future

Argument

• KF1. If you are not justified in believing that FLP is true, then your belief that the sun will set in the west tomorrow is unjustified.
• KF2. You are not justified in believing that FLP is true.
• KF3. So, your belief that the sun will set in the west tomorrow is unjustified.
• KF4. If your belief that the sun will set in the west tomorrow is unjustified, then you don’t know that the sun will set in the west tomorrow.
• KF5. So, you don’t know that the sun will set in the west tomorrow.

This generalizes to any belief about the future. All of your beliefs about how things will be in the future are unjustified. You don’t know what’s going to happen one year from now, one hour from now, or even one second from now.

Knowledge and Justification

Argument

• KF4. If your belief that the sun will set in the west tomorrow is unjustified, then you don’t know that the sun will set in the west tomorrow.

What is the difference between a belief that happens to be true and knowledge?

• lucky guesses: urn examples.
• do you believe that there are snakes in Hawaii?
• confidently bad at math example

KF1 and FLP

The Faulty Foundation Argument

• FF1. Your belief that the sun will set in the west tomorrow is based on FLP.
• FF2. If a belief is based on something that you aren’t justified in believing, then that belief itself is unjustified.
• KF1. So, if you are not justified in believing that FLP is true, then your belief that the sun will set in the west tomorrow is unjustified.

if they get hung up on ways that the future won’t resemble the past:

Future Like Past in Expected Ways (FLP*)

Future states of the world will be like past states of the world except in respects in which we can expect them to differ.

If they are wondering about FF2, give them power pose:

POWER POSE

Jared is getting ready for a job interview, and thinks it will help his chances if he spends five minutes “power posing” in front of the mirror. When his fiancée Ashley asks him why he thinks that will help, Jared tells her that scientists have shown that power posing releases performance-enhancing hormones into your bloodstream. Skeptical, Ashley does some Googling and informs Jared that the power-posing study has been completely discredited and is now widely regarded as “pseudo-science.”

KF2 and trouble for FLP

FLP is Unjustified

• UJ1. If your belief in FLP is justified, then it is either justified by direct observation or by inductive reasoning.
• UJ2. Your belief in FLP isn’t justified by direct observation.
• UJ3. Your belief in FLP isn’t justified by inductive reasoning.
• KF2. So, your belief in FLP is unjustified.

The key here is UJ3.

UJ1: There are other sources of knowledge—introspection, mathematical proof. But these won’t get you knowledge of the external world.

UJ2: You cannot directly observe the future.

Refection question:

1. The argument turns on the claim that induction and direct observation are the only ways of knowing about the world. Is that true? When a detective solves a crime unlike any crime she’s ever seen before, is she using resources other than induction and direct observation? If so, how might that help with resisting the argument?

The Anti-Circularity Argument for UJ3

Argument

• AC1. All inductive reasoning about the future assumes the truth of FLP.
• AC2. If all inductive reasoning about the future assumes the truth of FLP, then any inductive reasoning about FLP is circular.
• AC3. No belief can be justified by circular reasoning.
• UJ3. So, FLP isn’t justified by inductive reasoning.

AC2: Circularity: when the conclusion also appears as a premise.

AC3: Using the Magic 8-Ball to check whether the Magic 8-Ball can be trusted. Asking ChatGPT if what it just said is actually true.