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You'll lose weight if and only if you burn more calories than you take in.All those diet-plan books can never get around this, and all their details are pointless.
True, calorie intake and expenditure solely determine weight loss/gain. But after some thought, we can get examples where the above logicoverlooks some relevant differences: If your friend told you they were switching from a diet of2000 calories of balanced short-term and long-term energy sources (sugars, proteins, and carbs) to a diet of2000 calories worth of Pixy Stix at breakfast plus a Flintstones multivitamin,would you be optimistic that they would have the willpower to strictly follow the new plan?The two plans are equal when counting calories, but in actuality one really is a better plan.(Even more exaggeratedly, consider a daily plan of 2000 calories of sugar while never drinking any watersince water has no calories, it can't affect your calorie count,according to the above claim.)
These contrived counterexamples help illustrate that it's conceivable that there can be a difference between diet plans, so the initial claim isn't technically true.
The point illustrated is that often real-world arguments incorrectlyimply that their result follows from the form of the argument, when in fact the form is not valid in the way a syllogism is.This fallacy can be illuminated by finding a different domain in which the argument fails.The practice of searching for domains which invalidate the argument can help both sides of a debate hone inon bringing the unspoken assumptions to light. The original argument, if its conclusion is indeed true,must be patched either by adding the unspoken assumptions or fixing the invalid form.
Mistakes in syllogisms are hard to make: what are the only two ways to have an error in a syllogism?
| 1 | All people don't know my file's password. | Premise (Equivalent toNobody knows my file's password, but reworded to be of the required formAll somethings have some property..) |
| 2 | All hackers are people. | Premise |
| 3 | Therefore, my file is secure from hackers. | Incorrect syllogism, lines 1,2 |
| 1 | All people don't know my file's password. | Premise, but possibly false |
| 2 | All hackers are people. | Premise, but possibly false |
| 3 | Therefore, all hackers don't know my file's password. | Syllogism, lines 1,2 |
Of course, even if a proof fails, the conclusion might be true for other reasons.An incorrect argument doesn't prove the conclusion's opposite!
Of course, there are more ways to deduce things, beyond a syllogism.
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