SOLUTION: Use a Euler diagram to determine whether the syllogism is valid or invalid All cats have whiskers . All things with whiskers are dogs. ___________ ___________ ______ All cat

We look at the first premise:

We begin by drawing a circle representing all cats.

 

Since it says all cats have whiskers, we draw a larger circle that
represents all whiskered things, so that it completely encloses the 
circle that represents cats.

 

Next we look at the second premise:

[Note: a premise does not have to be true in real life, 
as this one.  However since it is a premise we assume
it anyway!]

Since it says all whiskered things are dogs, we draw a larger 
circle that represents all dogs, so that it completely encloses 
the circle that represents whiskered things.


 

Finally we look at the conclusion:

Then we determine whether this conclusion
is true based on the assumed premises.

So we look at the Euler diagram and ask ourselves the question

Is the circle representing all cats totally inside the circle
representing all dogs?

The answer is "yes", so the argument is valid.

Edwin