What is this fallacy?

[SenorBeef]

@AskNott

Maybe I’m wrong, but I think it might be (what was originally called) begging the question. That is, the starting premise includes what you intend to prove.

These days, the phrase “begging the question” is widely given a different meaning. It causes screaming and gnashing of teeth among word carvers. The new meaning is so widespread that some of us have surrendered to the change.

“Circular reasoning” is effectively the equivelant without any real loss of meaning, and it’s a lot more intuitively clear as to what you mean.

[Sage_Rat]

False premise

[chrisk]

@Indistinguishable

Which of the following arguments are meaningful and which are meaningless?

Argument #1:
Premise 1: I like strawberries
Premise 2: I like bananas
Cocnlusion: I like strawberries and I like bananas

Argument #2:
Premise 1: I like strawberries and I like bananas
Conclusion: I like strawberries

Argument #3:
Premise 1: I like strawberries
Conclusion: I like strawberries or I like bananas (perhaps both)

Argument #4
Premise 1: In my left hand, I have 5 strawberries
Premise 2: In my right hand, I have 2 strawberries
Conclusion: In my hands, I have 7 strawberries

Argument #5
Premise 1: I have 4 bananas
Conclusion: I have an even number of bananas

I could well imagine any of these arguments being labelled with the accusation of “begging the question” or “valid but vacuously circular”, particularly if one were to present them less formally so that some of the premises become enthymematic, and yet I could also just as well imagine construing each of these as quite “meaningful”. For that matter, I can also imagine construing them as “meaningless”, and also construing the OP as “meaningless”. It all depends on the context. I don’t think there are grounds for some principledly sharp distinction between “meaningful” and “meaningless” in the way you apparently mean, nor any corresponding distinction between the kind of “The conclusion is implicitly there in the premises” which is requisite for any argument to be valid and the kind which we would label question-begging. It’s in the eye of the beholder, the use to which the argument is being put, the extent to which it could possibly be persuasive or a novel discovery, and so on.

I think I agree with your point. All of these are very useful deductive steps, even if they seem obvious when used by themselves. We learned names for 1-3 in mathematical logic in university:
#1: ‘and’ introduction.
#2: ‘and’ elimination.
#3: ‘or’ introduction.

#4 could be the principle of addition, and #5 is based on the mathematical property of ‘evenness’.

[Indistinguishable]

@Bisected8

Nope, there are formal definitions for an accurate (“Sound”) argument.

What are you saying “Nope” to? I didn’t say there weren’t formal definitions of “sound” (though I could get into some debate over the relativity of that definition if you liked as well, but it has nothing to do with this); I said there weren’t very sharp formal definitions for “begging the question”. At least, not ones which always distinguished between those valid arguments we would consider significant and those valid arguments we would consider vacuous, as such determination of an argument’s usefulness could depend on a variety of factors external to the argument itself, that being some of what I tried to illustrate with that post.

[AHunter3]

If you are in an insane asylum, you must be crazy.
You’re in an insane asylum.
Therefore you must be are crazy.

Rephrased:

If you are crazy you belong in an insane asylum
You are in an insane asylum
Therefore you must be crazy
That’s the real construct, and yes it is a fallacy.

Elaborated:

If you are crazy you belong in an insane asylum
Crazy people are incapable of making the determination of whether or not they are crazy
You are in an insane asylum
Therefore you must be crazy
You do not believe you are crazy
Therefore by exhibiting the inability to properly make the determination that you are crazy, we know for sure that you are crazy

[aldiboronti]

The study of formal logic is a real eye-opener. You look and listen to the media with a new awareness and begin noting all the invalid arguments out there. And they are legion!

[ashman165]

@Bisected8

Nope, there are formal definitions for an accurate (“Sound”) argument. A sound argument has to be both valid and true. Which for the purpose of logic are defined as;

Valid: To be valid the chain of reasoning must be sound. The logic used must be effective and…well…logical. An argument with invalid logic is a fallocy.
Truth: For an argument to be “true”, the premises must be true, note that a faulty premise can still result in a true conclusion. The later case does not make an argument true.
Sound: If the argument is both valid and true then it can be considered a sound argument. If it has just one or the other or neither, it isn’t sound.

Bolding is mine. That’s not the case. You can’t use the word sound in the definition of sound and valid.

The validity of an argument is derived exclusively by form.
The soundness of an argument deals with the truth of premises.

A valid argument can be false, but that’s immaterial because at that level of analysis, we restrict ourselves to form. Does the conclusion flow from the stated premises.

A sound argument, on the other hand, can never be false because it a.) must already be valid (form), and factually true. Otherwise, the argument isn’t sound.

OP’s argument (while suffering from a grammar error) is valid. The conclusion flows from the stated premises. It has the form of a proper syllogism.

It is, however, factually not true because there exists such a condition necessarily rejected by the first premise, which is that inside the facility will be found staff. It’s highly improbable that all staff will be insane; there might even be a janitor there who is sane. So, the first premise is quite false, but the structure of the argument (other than the grammar) is fundamentally valid.