When is black not black

Recently I received a forwarded email that included several glib statements and an unflattering photo-shopped picture of President Obama.  The sentences are included at he end.  The author challenged me to read the sentences and think of a reason why I shouldn’t pass them on.

With that thought in mind I got out an old textbook that has a chapter on propositional logic.  Compound propositional sentences express logical relationships between the simpler sentences that compose them.  If my explanation is not clear (very likely) you can find many references in your library or on the Internet.  These methods are important in the process of critical thinking and help us see where authors and/or advertisers are trying to lead us.  In fact we often apply them without thinking about it.

The sentences often include or imply the following connectors.

“and”, “or”, “if…then”, “if and only if”, “not”


Assumption 1:  All Cats are black.  Assumption 2:  John has a cat.

This is an easy one.  I make two assumptions, one that all cats are black, and two that John has a cat.  From these two assumptions the only conclusion I can reach is that “John’s cat is black” (if..then).  Based on the assumptions I made this is a logically true statement even though in the ‘real’ world all cats are not black.  This example brings up a very important concept in propositional logic.  That is, a conditional sentence may be logically true even if one or more of the assumptions is not valid.

It is our job to go beyond the structure of the sentences and try to determine if the underlying assumptions are actually valid in the real world and if the conclusion we draw from those assumptions is also valid.  In a future blog entry I am hoping to provide a professional analysis of each one of these sentences,  In the meantime I encourage everyone to look at each one carefully.  Remember that your own bias will weigh heavily in your analysis so just try to apply the rules of logic.

My point here is that it’s important that we all evaluate everything we read so we can see where the author is trying to lead us.  We ask our children to use critical thinking when evaluating what they see and hear yet we are so easily manipulated ourselves by hasty generalizations, irrelevant conclusions, non sequiturs and other fallacious arguments designed to obscure the real issues and problems.  Party affiliation aside I think we owe it to future generations to not let ourselves be seduced by a few sound bites or glib sentences.

In conclusion, what can I say about a photo-shopped picture of the president to help illustrate the author’s version of future events.  I assure you I can find many pictures of past presidents, republican and democrat alike that do not require Photoshop to illustrate their ‘actual’ short falls.

Happy Holidays


PS   More to come.

Sentences to analyze:

1. You cannot legislate the poor into prosperity, by legislating the wealth out of prosperity.

2. What one person receives without working for, another person must work for without receiving.

3. The government cannot give to anybody anything that the government does not first take from somebody else.

4. You cannot multiply wealth by dividing it.

5. When half of the people get the idea that they do not have to work because the other half is going to take care of them; and when the other half gets the idea that it does no good to work, because somebody else is going to get what they work for, that is the beginning of the end of any nation.

Following these sentences was a photo-shopped picture of President Obama standing in a barren landscape with the caption “My work is done here”.


3 thoughts on “When is black not black

  1. Jim Dewar

    Yeesh. As important as the propositional logic in analyzing these sentences is the definition of words. The words here are used more for effect than for communication or argumentation. #4, for example, plays on the mathematical terms ‘multiply’ and ‘divide’, but doesn’t provide clear indications of what multiplying wealth or dividing it mean. If you reword it to say “you cannot increase wealth by distributing it among the poor” the sentence loses its punch entirely without straying too far from what I perceive to be its intended message. And neither side of the political divide owns a monopoly on this kind of loose rhetoric.


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