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Logical Fallacies

I love Logical Fallacies.
Well, to be clear,  I love the idea of Logical Fallacies, specifically the fact that over the ages people have analyzed and classified the many ways that individuals can intentionally, or unconsciously and unintentionally, make argue in illogical or misleading ways. For my benefit, I thought I would write a series of essays evaluating the different classes and specifics of Logical Fallacies.
Since the time of the greeks and romans Logic, Rhetoric and Philosophy were formal subjects of study in every well rounded education. As we all recall from school, the first step to teach anything is break it down into little pieces and then group all the pieces together as you try and reconstruct the whole.  Speaking as a biochemist, I have to admit this doesn't always work that well, but following in the footsteps of the ancients, let's give that a try.

Formal Logical Fallacies

In the sub-discipline of Philosophy concerned with logic, in order to be considered true and correct, an argument must be both sound and valid.  An argument is valid if it is based on a correct formal structure.  In other words, IF the premises are true THEN the conclusion must be true. When many of us think of formal logic, its probably this characteristic that comes to mind. However,  a valid argument may or may not be true depending or whether the premises are sound.   A valid argument will be correct and true if the premises are correct and true or sound. 
Thus, Formal Logical Fallacies arise when a structure of a logical argument is not valid.
Formally and abstractly, a classic example is the following.
  1. If A then B
  2. A
  3. Therefore B
However, a logical fallacy for this would be: 
  1. If A then B
  2. B
  3. Therefore A
For example, a valid example would be
  1. If it is daytime, the room will be bright
  2. It's daytime
  3. Therefore, the room is bright.
Invalidly,  
  1. If it is daytime, the room will be bright
  2. The room is bright
  3. Therefore, it must be daylight.  
This isn't the only possibility. I could have turned on the light, the drapes could be on fire, the room could be full of fireflies. 

Informal Logical Fallacies

In contrast, to Formal Logical Fallacies  Informal Logical Fallacies owe their wrongness not to the lack of validity in their logical structure, but rather in either the soundness or misuse of their premises. More broadly statement, their premises fail to support their conclusions.
Informal Logical Fallacies can be very tricky and their character varied. They great names like "Red Herring", "No True Scotsman", "Strawman" and "Ad Hominem".   I'll go into detail in a subsequent post.  Curiously, I think that almost all of them can be illustrated with statements made in the last year by someone in the Trump Administration. 

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