What is your answer?
If you overslept, you'll be late.
You aren't late.
So ???
{ 1 } - You didn't oversleep.
{ 2 } - You're late.
{ 3 } - You did oversleep.
{ 4 } - None of these validly follows.
<= back | menu | forward =>
Directions: Click on a number from 1 to 4.
1 is correct!
If you overslept, you'll be late.
You aren't late.
So ???
{ 1 } - You didn't oversleep.
{ 2 } - You're late.
{ 3 } - You did oversleep.
{ 4 } - None of these validly follows.
Logicians call this form MODUS TOLLENS (denying mode). The general idea is that whatever implies something that is false is itself false:
If A then B. VALID
Not-B.
So not-A.
<= back | menu | forward =>
Before continuing, you might try some wrong answers.
2 is wrong. Please try again.
If you overslept, you'll be late.
You aren't late.
So ???
{ 1 } - You didn't oversleep.
{ 2 } - You're late.
{ 3 } - You did oversleep.
{ 4 } - None of these validly follows.
Huh? The second premise says that you aren't late!
<= back | menu | forward =>
3 is wrong. Please try again.
If you overslept, you'll be late.
You aren't late.
So ???
{ 1 } - You didn't oversleep.
{ 2 } - You're late.
{ 3 } - You did oversleep.
{ 4 } - None of these validly follows.
Given the premises, "You did oversleep" has to be false.
<= back | menu | forward =>
4 is wrong. Please try again.
If you overslept, you'll be late.
You aren't late.
So ???
{ 1 } - You didn't oversleep.
{ 2 } - You're late.
{ 3 } - You did oversleep.
{ 4 } - None of these validly follows.
No, we can draw one of the conclusions.
<= back | menu | forward =>
the end