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Originally published 2015-11-11. Revised with additions on 2023-11-17, for a posting on academia.edu.
Preface
BLACKBURN, SIMON (1996) Oxford Dictionary of Philosophy, Oxford, Oxford University Press.
PIRIE, MADSEN (2006)(2015) How To Win Every Argument, Bloomsbury, London.
Blackburn explains 'Any proposition of the form 'if p then q'. The condition hypothesized, p, is called the antecedent of the conditional, and q the consequent'. Blackburn (1996: 73).
According to Blackburn conditional equates to consequent.
BLACKBURN, SIMON (1996) Oxford Dictionary of Philosophy, Oxford, Oxford University Press.
PIRIE, MADSEN (2006)(2015) How To Win Every Argument, Bloomsbury, London.
Blackburn explains 'Any proposition of the form 'if p then q'. The condition hypothesized, p, is called the antecedent of the conditional, and q the consequent'. Blackburn (1996: 73).
According to Blackburn conditional equates to consequent.
Affirming The Consequent Fallacy
Pirie writes affirming the consequent fallacy is natural for those that confuse 'the order of horses and carts'. Pirie (2006)(2015: 35).
His example
'When cats are bitten by rabid hedgehogs they die. Here is a dead cat, so obviously, there is a rabid hedgehog about'. (35).
The author explains that there are other overlooked reasons for the death of the cat such as being hit by a vehicle or electrocuted. The death of the cat from a rabid hedgehog cannot be reasonably deduced as fact. (35).
It is proper to affirm the antecedent (p from Blackburn) to prove (q) the consequent, but not vice-versa. (35).
So, using his example, when cats are bitten by a rabid hedgehog they die (or when cats are infected by rabies, my add) (p), but the (q) cannot be affirmed to prove (p).
There are many possible reasons for a deceased feline.
Interestingly, Pirie notes that this fallacy is used in the legal system, the courts, as the basis for circumstantial evidence.
For example, based on his examples.
If John wanted to kill his wife Joan, he would have taken out an extra life insurance on Joan.
John did take out extra life insurance on Joan.
Or,
If John had wanted to poison Joan to death, he would have bought poison.
John did buy poison.
Pirie writes affirming the consequent fallacy is natural for those that confuse 'the order of horses and carts'. Pirie (2006)(2015: 35).
His example
'When cats are bitten by rabid hedgehogs they die. Here is a dead cat, so obviously, there is a rabid hedgehog about'. (35).
The author explains that there are other overlooked reasons for the death of the cat such as being hit by a vehicle or electrocuted. The death of the cat from a rabid hedgehog cannot be reasonably deduced as fact. (35).
It is proper to affirm the antecedent (p from Blackburn) to prove (q) the consequent, but not vice-versa. (35).
So, using his example, when cats are bitten by a rabid hedgehog they die (or when cats are infected by rabies, my add) (p), but the (q) cannot be affirmed to prove (p).
There are many possible reasons for a deceased feline.
Interestingly, Pirie notes that this fallacy is used in the legal system, the courts, as the basis for circumstantial evidence.
For example, based on his examples.
If John wanted to kill his wife Joan, he would have taken out an extra life insurance on Joan.
John did take out extra life insurance on Joan.
Or,
If John had wanted to poison Joan to death, he would have bought poison.
John did buy poison.
These both have alternate explanations (37) but when these mount up it becomes easier for a court to find someone guilty of a crime. (37).
Pirie writes that this fallacy under review, is used to impute motives to a person. (37). This could be committed in a legal and court context, or like to find guilt with someone.
Perhaps in truth, perhaps in error.
Logically fallacious: Affirming the Consequent
Cited
'Description: An error in formal logic where if the consequent is said to be true, the antecedent is said to be true, as a result.
Logical Form: If P then Q. Q. Therefore, P. Example #1: If taxes are lowered, I will have more money to spend. I have more money to spend. Therefore, taxes must have been lowered.
Explanation: I could have had more money to spend simply because I gave up crack-cocaine, prostitute solicitation, and baby-seal-clubbing expeditions.'
'References: Jevons, W. S. (1872). Elementary lessons in logic: deductive and inductive : with copious questions and examples, and a vocabulary of logical terms. Macmillan.'
(Quite the examples from the website...)
Cited
'“Affirming the Consequent” is the name of an invalid conditional argument form. You can think of it as the invalid version of modus ponens.
Below is modus ponens, which is valid:
1. If A then B
2. A
Therefore, B
Now, below is the invalid form that you get when you try to infer the antecedent by affirming the consequent:
1. If A then B
2. B
Therefore, A
No matter what claims you substitute for A and B, any argument that has the form of I will be valid, and any argument that AFFIRMS THE CONSEQUENT will be INVALID.
Remember, what it means to say that an argument is invalid is that IF the premises are all true, the conclusion could still be false. In other words, the truth of the premises does not guarantee the truth of the conclusion.
Here’s an example:
1. If I have the flu then I’ll have a fever.
2. I have a fever.
Therefore, I have the flu.
Here we’re affirming that the consequent is true, and from this, inferring that the antecedent is also true.
But it’s obvious that the conclusion doesn’t have to be true. Lots of different illnesses can give rise to a fever, so from the fact that you’ve got a fever there’s no guarantee that you’ve got the flu.'
(Yes, sadly I had the mumps and a fever as a child)
(Therefore a valid deductive argument can have:
False premises and a true conclusion (FT)
False premises and a false conclusion (FF)
True premises and a true conclusion (TT)
However... True premises and a false conclusion (TF) is invalid
Valid arguments with all true premises are called sound arguments
These also have true conclusions)
---
Cumulative evidences
In PhD thesis research, this fallacy connects to cumulative evidences. One evidence by itself may not lead to a reasonable conclusion, but the more cumulative evidences there are, the more reasonable a conclusion.
From a Biblical perspective, historical Scriptural evidences for the existence of the triune God, Christ and the Gospel can be used, primarily in an attempt to demonstrate Christianity as a reasonable or most reasonable worldview, philosophy, theology.
Secondarily, theistic philosophical (philosophy of religion) evidences such as the idea as necessary for an infinite, eternal, first cause can also be used, although they do not prove the Biblical God, they support the existence of such a creator.
Therefore the secondary cumulative evidences can support the primary cumulative evidences.
But this should not be done affirming the consequent fallacy.
I would NOT state simply...
(A) An infinite, eternal, first cause, is necessary (antecedent)
(b) The eternal Biblical God is documented in scripture (consequent)
A to B exists (yes, both A and B exist)
Therefore
B to A means B is A (affirming the consequent fallacy)
All is correct until the therefore...
More premises are required in support of B = A.
Deism and other forms of theism are other worldviews and philosophical and theological possibilities. But these propositions and evidences must be reasonably and accurately compared to the propositions, and conclusions, the evidences, for Biblical Christianity. Through my MPhil and PhD theses research, and my website research and articles, I have connected the historical, Scriptural God to philosophy of religion concepts. I do reason that within reasonable, but not absolute certainty, internally and externally the premises in support of Biblical Christianity as a worldview are superior to premises in support of any other worldview. Therefore Biblical Christianity is true. Note, from my archives, only the infinite God has absolute, 100% certainty.
But reviews of, and comparisons to, other worldviews have taken place. Even without admittedly complete objectivity, having been a biblical Christian from a very young age, this was done with the use of reasoning, prayer, considering propositions and then premises and conclusions as evidence.
BLACKBURN, SIMON (1996) Oxford Dictionary of Philosophy, Oxford, Oxford University Press.
LANGER, SUSANNE K (1953)(1967) An Introduction to Symbolic Logic, Dover Publications, New York. (Philosophy).
PIRIE, MADSEN (2006)(2015) How To Win Every Argument, Bloomsbury, London.
