Logical fallacies: Learn them, avoid them, and point them out viciously in other people's arguments.
Cherry picking: Always put forth and refute opposing views.
Occam's Razor: When various possible solutions have equal likelihood of being true, choose the simplier one to remove what is superflous. This really helps to combat pseudoscience, the New Age, etc.
Scientific method: The best way we know to discover the truths of reality, and the best standard to hold claims of new knowledge to.
Freethought: Not so much a tool but more of a personal philosophy of logic.
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