I'm John Halpin

And your textbook is The Logic Cafe...an online textbook plus a virtual teaching assistant. We'll see how it works!


  • There's lots to do with your computer to learn logic. The Cafe is a multimedia experience...it will talk you through your work.
  • Even the textbook comes a bit alive from time to time.
  • There is instant checking of your homework.
  • Mandatory Warning: Though the course is fun when you keep up, there are problems when you don't. So, plan on lots of time...

Let's think about Logic first, try to see what it is, then return to the course details.

So, What is logic?



There are lots of ways to think about correctness of reasoning. We'll be interested in the FORM of argumentation. So we'll SYMBOLIZE. For example:




Notice that this reasoning is broken up into parts. You may be aware of this sort of terminology:

  • Premises
  • Conclusion (note the indicator)
  • Argument

We'll symbolize an argument in various ways, that's to abbreviate the details to get at the important part of the reasoning. Premise One:




Or, in our symbols:






Final Points on Symbols

We will see that arguments of SL can get fairly complicated and difficult.

Also, we will symbolize arguments for which we need to look at more than the logic of compound sentences.

Example: "Every country has a leader" --> (^x)(Cx>(%y)Lyx)

We symbolize to abbreviate and get at essentials of our thinking/logic.


Another Example:



Premises? Conclusion? Indicators?

Standard Form:





Next Topic:

ARGUMENT STRENGTH...what makes a good argument?

Think about some examples:










We will call 1 and 2 "valid"




Here's the idea: You can't coherently imagine it happening. Not just that you know it didn't happen. It’s inescapable given the evidence.

Note: 1 and 2 are valid according to this definition.

But 1 is better. WHY?





(Idea: garbage in, garbage out.)



More examples:

4) I own a "normal" house, with a normal attic.
There are "pitter-patter" noises coming from
the ceiling.
I conclude that Rodents inhabit my attic.

5) There are over one million tickets to the
Chris owns exactly one of them.
The one winning ticket will be selected at random.
So, Chris will not win.

There's something right about this sort of thinking. But it's not as though these arguments are valid. Their conclusion says somethig more than do their premises. Each argument takes certain evidenc and draws a conclusion that is new.




Note: this "inductive" argumentation is not much treated in this class.

(Ampliative vs. Conservative thinking)



next lecture...