PHL111 Valid Reasoning, Past Assignments
Reading: Read chapter 1 of CIL.
Practice: Hand in at the beginning of class your answers
to problems 1-5 at the end of chapter 1. Each of these problems
asks you to come up with 5 examples; to make the homework
shorter, for each problem just come up with 2 examples.
Handwritten is acceptable (for many of our later homeworks there
are special symbols or tables and it is too much work to try to
Reading: Read chapter 2 of the book.
Practice: Complete problems 5 and 6 at the end of chapter 2.
(I've been asked about how to do this. For each problem (that, is
for 5 and then for 6) make one translation key,
showing what each atomic sentence letter means in English. Each
atomic sentence in your key should correspond to an atomic sentence
in English. So, look through the problems in 5 (a-j), identify all
the atomic sentences, write them down, and tell me which letter
corresponds to each sentence. Your key will look like:
Then, after having done that, and using your key, translate all
those sentences. Do the same again for 6.)
P: Josie is a cat.
Q: Josie is a mammal.
R: Josie is a fish
Philosophy club meets at 4:30pm in MCC 211.
The meeting will be a showing of the 2017 movie Annihilation.
Read chapter 3 of our textbook.
Homework listed below! Two quick points.
* A reminder: we have a no-phones, no computers policy in class. I
know that's hard! We are all used to checking snapchat or scores
or whatever every ten seconds. But psychologists have proven that
no one is good at multi-tasking--you will inevitably miss out if
you cruise the web during class, and the people around you will be
distracted too. I don't grade for attendance, so you can skip
class without penalty if you need to text or watch some video or
whatever. My goal is to create a place and time where we all try
to be focussed, that's all. Thanks!
* I defined "argument" in a very thin way: as an ordered list of
sentences, one of which we call the conclusion, and the others
which we call premises. Then, we distinguish good from bad
arguments by saying the valid arguments are the good ones; all
arguments that are not valid are bad. But sometimes in colloquial
English people use "argument" to mean an argument that is valid or
that at least has some other good feature. Here is a famous
example (at 2:15)!
Homework: Since our last translations didn't go so well,
let's try again.
Translate the following sentences from English into our logical
language, the Propositional Logic. Provide one key for the entire
assignment that shows to which (hopefully atomic) English
sentences your propositional logic sentence letters correspond.
Always try to show as much as you can about the structure of the
sentence in our logic (that is, don't translate them all as a
single letter, like P). Hand in your answers and translation key
at the beginning of class. Write your homework neatly, since I
might want to show yours on the overhead as an example.
For these problems: The last one is hard! It nests
"if... then..."s. Try it. Also, think hard about "material" and
"immaterial" -- can you show their relation using our logic (using
one idea standing for "material")? It would be best if you could.
Number 9 is tricky. Remember our discussion of "only if."
What do we mean by
"translation key"? We mean a translation from English to
our logical language. Suppose instead one of
our sentences was....
- The mind is brain activity.
- The mind is material.
- The mind is immaterial.
- If the mind is immaterial, then the mind is not
- If mind is brain activity, then the mind is material.
- Provided the mind is not immaterial,
then the mind is brain activity.
- Alzheimers is a disease of the mind.
- If the mind is brain activity,
then Alzheimers is a disease of the brain.
- The mind is brain activity only if the mind is material.
- If the mind is brain activity,
then Alzheimers is a disease of the mind
only if Alzheimers is a disease of the brain.
8. Spongebob pays no property taxes, if Spongebob lives in
You identify the atomic sentences inside that complex sentence,
and then make a key. There are two atomic sentences in this
sentence, so your key would include the following:
English ..................................... Propositional Logic
Note that we took out the negation. We want to handle negations
with our "¬" symbol. And then if you translated the sentence:
Spongebob lives in Bikini Bottom........... P
Spongebob pays property taxes........... Q
8. (P → ¬ Q)
Someone would be able to use your key to determine
how to translate your logical sentence back into an
equivalent English sentence.
So, for this homework, you'll write instead one key (put it at
the top of the page), which will have a column of atomic
English sentences, and beside it a column of atomic logic
sentences (P, Q, R....). Then, and only then, write up the