FORMAL FALLACY
In philosophy, a formal fallacy or a logical fallacy is a pattern of reasoning which is always wrong. This is due to a flaw in the structure of the argument which renders the argument invalid. A formal fallacy is contrasted with an informal fallacy, which may have a valid logical form, but be false due to the characteristics of its premises, or its justification structure.
The term fallacy is often used more generally to mean an argument which is problematic for any reason, whether it be a formal or an informal fallacy.
Kinds of fallacies:
1. The appeal to probability is a logical fallacy. It assumes that because something could happen, it is inevitable that it will happen. This is flawed logic, regardless of the likelihood of the event in question. The fallacy is often used to exploit paranoia
Ex. There are many hackers that use the internet. Therefore, if you use the internet without a firewall, it is inevitable that you will be hacked sooner or later."
2. The argument from fallacy, also known as argumentum ad logicam or fallacy fallacy, is a logical fallacy which assumes that if an argument is fallacious, its conclusion must be false.
Ex: "All cats are animals. Ginger is an animal. This means Ginger is a cat.".
3.The bare assertion fallacy is a fallacy in formal logic where a premise in an argument is assumed to be true merely because it says that it is true.
One form of the fallacy may be summarized as follows:
- Fact 1: X claims statement A.
- Fact 2: X claims that X is not lying.
- Conclusion: Therefore, A is true.
4.The conjunction fallacy is a logical fallacy that occurs when it is assumed that specific conditions are more probable than a single general one.
Ex. Linda is 31 years old, single, outspoken, and very bright. She majored in philosophy. As a student, she was deeply concerned with issues of discrimination and social justice, and also participated in anti-nuclear demonstrations.
Which is more probable?
1. Linda is a bank teller.
2. Linda is a bank teller and is active in the feminist movement.
5. A fallacy of necessity is a fallacy in the logic of a syllogism whereby a degree of unwarranted necessity is placed in the conclusion.
Ex. Bachelors are necessarily unmarried.
6. Negative proof, the fallacy of appealing to lack of proof of the negative, is a logical fallacy of the following form:
"X is true because there is no proof that X is false."
It is asserted that a proposition is true, only because it has not been proven false. The negative proof fallacy often occurs in the debate of the existence of supernatural phenomena, in the following form:
"A supernatural force must exist, because there is no proof that it does not exist".
PROPOSITIONAL FALLACIES
1. The logical fallacy of affirming a disjunct also known as the fallacy of the alternative disjunct occurs when a deductive argument takes either of the two following forms:
A or B
A
Therefore, it is not the case that B
A or B
B
Therefore, it is not the case that A
The fallacy lies in concluding that one disjunct must be false because the other disjunct is true; in fact they may both be true. A similar form that is valid has the second premise (rather than the conclusion) be a negation. The valid form is known as disjunctive syllogism.
Ex. It will rain somewhere tomorrow or the sun will shine somewhere tomorrow.
2. Affirming the consequent, sometimes called converse error, is a formal fallacy, committed by reasoning in the form:
If P, then Q.
Q.
Therefore, P.
Arguments of this form are invalid, in that arguments of this form do not always give good reason to establish their conclusions, even if their premises are true.
The name affirming the consequent derives from the premise Q, which affirms the "then" clause of the conditional premise.
If Bill Gates owns
Bill Gates is rich.
Therefore, Bill Gates owns
QUANTIFICATIONAL FALLICY
1. The existential fallacy, or existential instantiation, is a logical fallacy committed in a categorical syllogism that is invalid because it has two universal premises and a particular conclusion. In other words, for the conclusion to be true, at least one member of the class must exist, but the premises do not establish this.
All inhabitants of other planets are friendly, and all Martians are inhabitants of another planet. Therefore, there are friendly Martians. (The conclusion assumes there really are Martians in existence.)
2. Proof by example (also known as inappropriate generalisation) is a logical fallacy whereby one or more examples are claimed as "proof" for a more general statement.
This fallacy has the following argument form:
I know that x 
X has the property P.
Therefore, all other elements of X have the property P.
The following example demonstrates why this is a logical fallacy:
I've seen a person shoot someone dead.
Therefore, all people are murderers.
Conditional or questionable fallacies
1. The definist fallacy involves the confusion between two notions by defining one in terms of the other. G. E. Moore, for example, argued that "good" should not be defined in terms of "producing pleasure", because it would always make sense to ask of a pleasureable thing whether or not it was in fact good
Informal fallacy
1. An informal fallacy is an argument whose stated premises fail to support their proposed conclusion.[1] The deviation in an informal fallacy often stems from a flaw in the path of reasoning that links the premises to the conclusion.
Ad nauseam arguments are logical fallacies that rely upon the repetition of a single argument while ignoring other valid arguments, to counter those other arguments. This tactic relies on the use of intentional obfuscation, in which other logic and rationality is intentionally ignored in favor of preconceived, and ultimately, subjective modes of reasoning and rationality.
2. Appeal to ridicule, also called the Horse Laugh, is a logical fallacy which presents the opponent's argument in a way that appears ridiculous, often to the extent of creating a straw man of the actual argument. For example:
- If Einstein's theory of relativity is right, that would mean that when I drive my car it gets shorter and heavier the faster I go. That's crazy! (This is, in fact, true, but the effect is so minuscule a human observer will not notice.)
3. The argument from ignorance, also known as argumentum ad ignorantiam ("appeal to ignorance" ) or argument by lack of imagination, is a logical fallacy in which it is claimed that a premise is true only because it has not been proven false or is false only because it has not been proven true.
Ex. The solar system must be younger than a million years because even if the sun were made of solid coal and oxygen it would have burned up within that time at the rate it generates heat."
4.The fallacy of the single cause, also known as joint effect or causal oversimplification, is a logical fallacy of causation that occurs when it is assumed that there is one, simple cause of an outcome when in reality it may have been caused by a number of only jointly sufficient causes.
Often after a tragedy it is asked, "What was the cause of this?" Such language implies that there is one cause, when instead there were probably a large number of contributing factors. However, having produced a list of several contributing factors, it may be worthwhile to look for the strongest of the factors, or a single cause underlying several of them.
5.The practice of "quoting out of context", sometimes referred to as "contextomy," is a logical fallacy and type of false attribution in which a passage is removed from its surrounding matter in such a way as to distort its intended meaning. Quoting out of context is often a means to set up "straw man" arguments. Straw man arguments are arguments against a position which is not held by an opponent, but which may bear superficial similarity to the views of the opponent.
6. The perfect solution fallacy is a logical fallacy that occurs when an argument assumes that a perfect solution exists and/or that a solution should be rejected because some part of the problem would still exist after it was implemented.
Examples:
Posit (fallacious):
These anti-drunk driving ad campaigns are not going to work. People are still going to drink and drive no matter what.
Rebuttal:
Although the ads will not prevent every single instance of drunk driving, it would reduce the rate enough to make the policy worthwhile.
