1. Avoiding Ungrounded Assumptions
Chapter Eight
Avoiding Ungrounded Assumptions

2. Fallacies of Presumption
Fallacies of presumption take for granted (or presume) something that is in fact debatable.
Examples of Fallacies of Presumption:
Begging the Question
Begging the Question Against
Complex Question
False Alternatives
Accident

3. Begging the Question
The argument features at least one premise that itself depends on the conclusion’s being true, so that it can be accepted only if one has already accepted the conclusion.
When a valid (or even a sound) argument begs the question, its premises fail to offer compelling reasons for accepting its conclusion.
Any argument that begs the question fails to be cogent.
The conclusion of a question-begging argument may in fact be quite acceptable, but this would be for reasons other than those offered by that argument.

4. Circular Reasoning
All deductive arguments have some degree of circularity, since the information in the conclusion of such arguments is always included in the premises.
But, the context of a circular argument, together with the degree of circularity in it, can help to determine whether the argument begs the question.
Logical circularity, whether formal or conceptual, comes in degrees. Some valid arguments have more circularity than others. The more logically circular an argument is, the more likely it is to beg the question.

5. Types of Circularity

6. Burden of Proof

7. Cash Value of Knowing the Burden of Proof
If you know that the burden of proof is on you, you know you must discharge it by offering an adequate argument in support of your claim.
If you know that the burden of proof is on the other side, you can rest until a sound objection to your view has been offered.
If you know that you are defending a claim that is part of common sense, then you also know that the burden of proof is on any challenger.

8. How to Avoid Begging the Question
Given a valid argument with acceptable premises, ask whether the premises are more acceptable than the conclusion they’re offered to support.
If yes, the argument is cogent.
If no, it’s question-begging.

9. Begging the Question Against
The argument features at least one controversial premise that is assumed to be true but not argued for.
Note: when a claim is controversial, an argument that commits this fallacy is no help in discharging the burden of proof.
How to avoid Begging the Question Against
Don’t include any controversial statement among your premises without first offering adequate reasons for it.

10. Complex Question
The question either has an unsupported assumption built into it or is a conflation of two or more different questions.
Thus, the complex question is a pattern of mistake in asking a question that can be answered only by yes or no, but which assumes either:
that there is only one question when there are in fact two or more, each with its own answer, or
that some claim is true when in fact it is either false or, at the very least, doubtful.

11. How to Avoid the Complex Question
Beware of any yes/no question presupposing that, if the answer is yes, a questionable proposition P (for which no argument has been offered) follows, and if your answer is no, P also follows.

12. False Alternatives
An argument commits the fallacy of false alternatives if and only if it offers in its premises a disjunction presenting two extreme alternatives as the only ones possible, when in reality there are one or more others equally plausible,
False alternatives are a defect in reasoning that might affect an argument containing a disjunction as premise.
A disjunction is a compound proposition with two members or ‘disjuncts.’
An exclusive disjunction has the form either P or Q (but not both).

13. How to Avoid the Fallacy of False Alternatives
In evaluating an argument with a disjunctive premise, check that premise to see if:
It claims that the two extreme alternatives offered are the only possible ones.
The alternatives are assumed to be incompatible.
In reality, both (1) and (2) are false.
If these conditions are met, then the argument commits the fallacy of false alternatives.

14. Accident
Accident is another fallacy of presumption that can undermine arguments: it is committed when some ‘accidental’ or exceptional feature of the case at hand is overlooked.
The fallacy of accident is committed by an argument that treats a certain case as falling under a general rule or principle when in fact the case counts as an exception to it.

15. How to Avoid the Fallacy of Accident
Logical thinkers must bear in mind that even the best principles usually have exceptions.
If a principle is applied inappropriately—i.e., to a case that is rightly an exception—then a fallacy of accident has been committed.