Introduction Logic and Carnegie Mellon University 9th September 2015
Writing Assignments and Readings In this course we re going to be doing a lot of reading. As per the syllabus, you should be sure to complete the reading assigned before class on the day that it is due The writing assignments ask you questions about the reading set on Monday and Wednesday, so you need to make sure to do the reading to do well on the writing assignments
Lecture Notes The slides from lectures are posted online. Go to the Course Content tab on Blackboard and you ll see a folder for them there.
Aims for Today To learn some important tools philosophers use: 1 Logic (used to evaluate arguments) 2 experiments (used for all kinds of purposes!)
Terminology In philosophy we care about arguments that can be given in favor of a position (more so than the position itself) 1 All raptors are terrifying 2 Blue is a raptor 3 Blue is terrifying (1) (2) are premises (3) is the conclusion
Validity When we say that an argument is valid we mean...... that if its premises were true then its conclusion would have to be true (Perry et al., 2015, 9)
Validity 1 All raptors are terrifying 2 Blue is a raptor 3 Blue is terrifying This is a valid argument. If the premises are true, then the conclusion must be true.
Check Your Understanding Take 30 seconds (or less) to think about this question: Can a valid argument have a false conclusion?
Check Your Understanding Can a valid argument have a false conclusion? Yes! 1 All English prime ministers are squirrels 2 David Cameron is an English prime minister 3 David Cameron is a squirrel If the premises were true then the conclusion would also have to be true. But David Cameron is not a squirrel!
Check Your Understanding Take 30 seconds (or less) to think about this question: Can an invalid argument have a true conclusion?
Check Your Understanding Can an invalid argument have a true conclusion? Yes! 1 If Becky can vote then Becky is a US citizen 2 Becky cannot vote 3 Becky is not a US citizen This is an invalid argument (do you remember what fallacy it is an instance of?) but the conclusion is true-i am not a US citizen!
Soundness When we say that an argument is sound we mean...... that it is valid and has all true premises (Perry et al., 2015, 9) An unsound argument is either invalid, or is valid but has at least one false premise
Soundness Example of a sound argument: 1 Every integer > 1 is either prime or the product of prime factors 2 5987 is an integer > 1 3 5987 is either prime or the product of prime factors
More Terminology Sometimes arguments can fail to be valid (and thus fail to be sound) but should not be dismissed as bad arguments For example: 1 90% of visitors to Wikipedia only view content (i.e. they don t edit or create new material) 2 Jenny is a visitor to Wikipedia 3 Jenny only views content (and doesn t edit or create new material) like the one above are said to be strong
Strength When we call an argument strong we mean that it is invalid, but if all of its premises were true, then its conclusion would probably be true Strength can come in degrees An invalid argument that is not strong is said to be weak
Weakness Here s an example of a weak argument: 1 10% of visitors to Wikipedia create or edit material 2 Jenny is a visitor to Wikipedia 3 Jenny creates or edits material
Cogency We call an invalid argument cogent if it is strong and has all true premises For example: 1 82% of Americans between the ages of 18 and 34 have internet access 2 Miley Cyrus is an American between the ages of 18 and 34 3 Miley Cyrus has internet access
Cogency Here s an example of an invalid argument that is not cogent: 1 82% of Americans between the ages of 18 and 34 have internet access 2 Madonna is an American between the ages of 18 and 34 3 Madonna has internet access Why does it fail to be cogent?
Summary When asked to evaluate an argument, keep these concepts in mind: 1 Validity 2 Soundness 3 Strength 4 Cogency
The runaway train scenarios we discussed last week were examples of thought experiments When we conduct a thought experiment, we are engaging in hypothetical thinking In the runaway train scenarios, we were trying to figure out the right thing to do We also tried to figure out why most people thought the right thing to do was pull the lever, but not to push the fat man
Philosophers are not the only people who make use of thought experiments! Scientists, such as Galileo and even Einstein, made use of thought experiments in their work
The Infinitude of the Universe Lucretius (who was a first century BC poet) tried to show that the Universe is infinite by using the following thought experiment: Suppose that the Universe has a boundary. Then we can throw a spear at the boundary. If the spear passes through the boundary, then it isn t a real boundary. If the spear stops or bounces back at us, then there must be something on the other side (in space) that is causing this. Thus, again, the boundary is not a real boundary. Consequently there is no boundary to the Universe and so it must be infinite. Briefly discuss the above thought experiment with your neighbor? Do you agree with Lucretius? Why or why not?
The Infinitude of the Universe? Lucretius s thought experiment does not establish the conclusion he hoped it would! We now know that there are spaces which are finite but unbounded Simple example: a circle. If we move around the circumference we find no edges but it is a finite space
Moral of the Story Lucretius s example shows us that while thought experiments can be powerful, they can also go wrong! Some questions to ask when you re presented with a thought experiment: Does it make sense? Do we need additional info to draw a conclusion? If so, what info? What does the author use it to conclude? Can you reconstruct their argument? Is their argument good?
The Experience Machine Suppose that there were an experience machine that would give you any experience you desired. Super-duper neuropsychologists could stimulate your brain so that you would think and feel you were writing a great novel, or making a friend, or reading an interesting book. All the time you would be floating in a tank, with electrodes attached to your brain. Should you plug into this machine for life, preprogramming your life experiences? [...] Of course, while in the tank you won t know you re there; you ll think that it s all actually happening... (Nozick, 1974) Spend a few minutes discussing whether you would plug in (and more importantly, why or why not!) with your neighbor
Pleasure We can try to use the experience machine thought experiment to argue against the claim that pleasure is the only thing that matters 1 If pleasure is the only thing that matters, then we would want to plug into the experience machine 2 We do not want to plug into the experience machine 3 Pleasure is not the only thing that matters Together with your neighbor, think about the following questions: Do you agree with the conclusion? If so, what other things do you think matter? If not, how would you criticize the argument?
Other The Missing Shade of Blue: You ve not seen a particular shade of blue, but you ve seen shades slightly darker and slightly lighter. Can you imagine the missing shade in between? Memory Swap: Imagine you and your neighbor swapped memories. Who would be who? Duplicate People: Two exact duplicates of Captain Sisko are created by DS9 s transporter instead of just one. Are they both Captain Sisko? Is one the real Sisko? Are neither the real Sisko?
Exit Ticket Select one of the thought experiments that we discussed today and say what you would conclude from it. Please give a brief description of the thought experiment so we know which one you mean (e.g. the one where you have to decide whether to plug in to a machine that gives you pleasurable experiences )
Bibliography R. Nozick. Anarchy, State, and Utopia. Basic Books, 1974. J. Perry, M. Bratman, and J. Fischer. Logical toolkit. In J. Perry, M. Bratman, and J. Fischer, editors, Introduction : Classical and Contemporary Issues, pages 8 13. 2015.