Tag: logic

P only if Q….

Hi everyone,

I’m writing to follow up on a discussion we had in class today, regarding methods for translating conditional (“if…then”) statements from English to symbols.

We started with:

If it rained, the ground got wet.

Which we symbolized as

R -> W

Where R = “it rained” and W = “the ground got wet”.

We then got stuck on the phrase:

It rained only if the ground got wet.

The correct symbolic version of this is:

R -> W

just as it appeared in the slides, where R = “it rained” and W = “the ground got wet”, just as before.  This is counterintuitive, but true!

For a longer discussion, with some better examples, take a look at this page (otherwise, just memorize it!):



OpenLab #3: “Sentences”

Due Thursday, 9/20/18.  For this week’s writing assignment, take a look at the picture below called “Sentences.”  Read every sentence in the picture.  As you read, pay attention to your own stream of consciousness – what are the thoughts that pop into your head?  For full credit, respond to all 4 of the following items.

  1. Record two observations about the sentences in the picture – what do you notice / what’s something you find interesting / what popped into your head / what stood out.
  2. Choose one of the sentences in the picture (do NOT choose the same sentence as anyone else).  Type the sentence out “in quotes”, and then answer the following questions:
    a. Is it a statement (as discussed in class on Tuesday)?  Explain why or why not.
    b. Is it true or false? Explain in everyday English why or why not.
  3. Make up a sentence that you believe would fit into this picture.  Tell us the sentence, and then tell us whether it is a statement, and whether it is true or false.
  4. What connection (if any) does this assignment have to do with the work we are doing in class?

“Sentences” by Flickr user Eldeem