"Keep an open mind – but not so open that your brain falls out" -unknown
"Extraordinary claims require extraordinary evidence." -- Carl Sagan
"What can be asserted without evidence can also be dismissed without evidence." -- Christopher Hitchens
What is a logical fallacy? All arguments have the same basic structure: A therefore B. They begin with one or more premises (A), which is a fact or assumption upon which the argument is based. They then apply a logical principle (therefore) to arrive at a conclusion (B). An example of a logical principle is that of equivalence. For example, if you begin with the premises that A=B and B=C, you can apply the logical principle of equivalence to conclude that A=C. A logical fallacy is a false or incorrect logical principle. An argument that is based upon a logical fallacy is therefore not valid. It is important to note that if the logic of an argument is valid then the conclusion must also be valid, which means that if the premises are all true then the conclusion must also be true. Valid logic applied to one or more false premises, however, leads to an invalid argument. Also, if an argument is not valid the conclusion may, by chance, still be true. For a more thorough discussion of logical fallacies and how to structure a logical argument, see the New England Skeptical Society's article, How To Argue.
Top 20 Logical Fallacies (in alphabetical order) taken from -
"The most exciting phrase to hear in science, the one that heralds the most discoveries, is not "Eureka!" (I found it!) but That's funny..." -Isaac Asimov
The scientific world view is full of awe and wonder. Understanding how truly awesome the universe is – in its elegant complexity, its staggering beauty, and the many intricate systems of which it is comprised – gives a profound feeling of connectedness and sparks the imagination. And it has the advantage of being real. -Steven Novella
The glory which is built upon a lie soon becomes a most unpleasant incumbrance. How easy it is to make people believe a lie, and how hard it is to undo that work again. — Mark Twain