## A guy goes into a Jewel-store owned by a logician who never lies...

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Also, it occurs to me that the clerk/logician, who never tells a lie, would have to lie to the police about whether the payment was made. So much for never lying.

Maybe he just prides himself on never lying to a customer.

Michael Ossipoff
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Presumably which one the clerk intended when he wrote it? Isn't that part of your theory on meaning; the speaker's intention? In this situation, the customer simply misunderstood.

The OP never said the clerk wrote the sign. As a matter of fact, the store owner (which isn't a logician) most likely wrote the sign because he is the one that actually owns the diamond.
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Because you're forgetting something important - the interpretation of the customer, which contradicts the clerk's interpretation. — Harry Hindu

Of course. That's why clerk's scam worked.

Yes the customer was intentionally deceived.
You're missing the point. The point is that the customer's interpretation of the sign is just as legitimate as the clerk's. The problem is that they both contradict each other, which means that at least one of the interpretations is wrong.They can't both be right at the same time.

Obviously the clerk's scam would be illegal. But, as I said, the customer has no proof that he paid for the diamond.
Of course he does. The diamond and the sign would attract attention. No other customers or clerks saw the customer give the clerk the money? There aren't cameras in the jewlery store? All these other behaviors you tell us the clerk engages to cover up the fact that the customer gave them the money in is dishonest. The clerk is a liar simply by his behavior.
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My objection to the predicate logic language was only that it seemed an unnecessary complication. If we're having a conversation, and you insist on speaking Latin, that doesn't mean that you're wrong, it just makes it more difficult for me. That was my complaint about predicate logic language.
Again you miss the point. It's not about speaking different languages, it's about using the correct terms in ANY langauge to translate to the correct terms of another language. When your logical system ends up being inconsistent with other logical systems, then something is wrong. They should all be integrated into a consistent whole.

You keep claiming that the clerk is a logician. If so, then the clerk would know that there other logical interpretations of the sign and that all logical interpretations should be consistent.
...but that could depend on the company that's using the computer.
You obviously don't know much about computer programming. ALL computer languages mean the same thing with IF-THEN statements.

The truth value of the implication-proposition is function of the truth-values of the premise and the conclusion.
No. It only depends on the truth value of the conclusion. Just look at the table.

But of course, by the standard implication truth-table, if the conclusion is true, the implication-proposition is true regardless of whether or not the premise is true.
Exactly. Now you've just contradicted your statement above. See how illogical this is?

But, as a practical matter, in the story, it doesn't matter. The customer can't prove that he paid, and so the scam worked. The clerk (who is also the store owner and a logician) can assure himself that he didn't lie when he scammed the customer, because his truth-table is the standard one.
You just keep moving the goal posts. This conversation is no longer meaningful.
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The OP never said the clerk wrote the sign. As a matter of fact, the store owner (which isn't a logician) most likely wrote the sign because he is the one that actually owns the diamond.

I said, in the title of the thread, that the store is owned by a logician. I said in my post that the clerk is the owner and logician.

Michael Ossipoff
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You're missing the point. The point is that the customer's interpretation of the sign is just as legitimate as the clerk's. The problem is that they both contradict each other, which means that at least one of the interpretations is wrong.They can't both be right at the same time.

The clerk's interpretation is correct, by the 2-valued truth-functional truth table and definition of implication that several academic sources were unanimous about.

There are other truth-tables for implication. I wouldn't say that some are more "legitimate" than others.

But the clerk's truth-table is the more widely-quoted one, the more standard one.

I'd said:

Obviously the clerk's scam would be illegal. But, as I said, the customer has no proof that he paid for the diamond.

You replied:

Of course he does. The diamond and the sign would attract attention. No other customers or clerks saw the customer give the clerk the money?

There was only one clerk in the store. But, as i said, he could have had an accomplice, to remove the money from the store before police arrived. There weren't other customers in the store.

There aren't cameras in the jewelry store?

I acknowledged that the security-camera would be a problem, maybe a prohibitive one.

I said, "Don't try this at home."

All these other behaviors you tell us the clerk engages to cover up the fact that the customer gave them the money in is dishonest. The clerk is a liar simply by his behavior.

Of course. He's a liar, because, even though he didn't lie to the customer, he lies to the police about whether the payment was made. So he doesn't really live up to the title of the thread.

And,even though he didn't lie to the customer, of course he defrauded and intentionally deceived the customer. His sign was false (a lie) when the clerk didn't honor it by keeping its promise. So, in that sense, too, the clerk lied (because he'd written and displayed the sign that proved false), even though his earlier assurance was true.

The scam couldn't be repeated. And, after the notoriety of the first time, the store wouldn't get any business. The scam wouldn't be very feasible, if do-able at all. And even if were feasible, it wouldn't be practical.

If he has a 20 million dollar diamond, why does he bother scamming for $5000? But the clerk didn't lie to the customer when he said the sign's implication-proposition was true, because that statement was correct,when made, by the standard truth-table for 2-valued truth-functional implication. Michael Ossipoff • 1.2k I’d said: . My objection to the predicate logic language was only that it seemed an unnecessary complication. If we're having a conversation, and you insist on speaking Latin, that doesn't mean that you're wrong, it just makes it more difficult for me. That was my complaint about predicate logic language. . You replied: . Again you miss the point. . I just keep missing that darn point! . It's not about speaking different languages . That was what my objection was about. . , it's about using the correct terms in ANY langauge to translate to the correct terms of another language. When your logical system ends up being inconsistent with other logical systems, then something is wrong. They should all be integrated into a consistent whole. . There are different truth-tables for implication. . You keep claiming that the clerk is a logician. If so, then the clerk would know that there other logical interpretations of the sign and that all logical interpretations should be consistent. . He was using the standard truth-table for 2-valued truth-functional implication. . I’d said: . ...but that could depend on the company that's using the computer. . You replied: . You obviously don't know much about computer programming. ALL computer languages mean the same thing with IF-THEN statements. . I didn’t say that different programming languages mean different things by IF-THEN. You said something about honesty, and that’s what I was replying to. There aren’t dishonest programming languages, but there are dishonest companies. And no doubt phishers and malware-writers use perfectly honest programming languages. . I’d said: . The truth value of the implication-proposition is function of the truth-values of the premise and the conclusion. . You replied: . No. It only depends on the truth value of the conclusion. Just look at the table. . Incorrect. . If the conclusion is false, then the truth of the implication depends on whether or not the premise is true, by the truth-table that I’ve been referring to, the standard 2-valued truth-functional truth-table. . I’d said: . But of course, by the standard implication truth-table, if the conclusion is true, the implication-proposition is true regardless of whether or not the premise is true. . You replied: . Exactly. Now you've just contradicted your statement above. . No, I didn’t. If the conclusion is false, then the implication proposition is false if its premise is true, and true if its premise is false. . You continued: . See how illogical this is? . You got that right. . I’d said: . But, as a practical matter, in the story, it doesn't matter. The customer can't prove that he paid [a problematic claim], and so the scam worked. The clerk (who is also the store owner and a logician) can assure himself that he didn't lie when he scammed the customer, because his truth-table is the standard one. Admittedly he'd have to lie to the police about whether the payment was made, and admittedly the implication-proposition in his sign was false (a lie) when he refused to give the diamond. But he didn't lie to the customer when he said that the sign's implication proposition was true before the payment was made. . You replied: . You just keep moving the goal posts. . Incorrect. That’s what I’ve been saying from the start. . This conversation is no longer meaningful. . It never was. . Michael Ossipoff • 1.2k But the clerk didn't lie to the customer when he said the sign's implication-proposition was true, because that statement was correct,when made, by the standard truth-table for 2-valued truth-functional implication. Whether or not the clerk lied isn't what is being argued against. My argument is that he isn't a logician. What I'm saying is that implication-propositions don't translate to logical "IF-THEN" statements that are used by people and computers via their programming. The customer interpreted the sign correctly as a causal relationship between the act of giving the money and the effect of receiving the diamond. If there is no relationship between the premise and the conclusion, then the sign is wrong to be written the way it is. • 1.2k My argument is that [the clerk] isn't a logician The clerk's interpretation that an implication-proposition is true if its premise is false is unanimously agreed on by the academic sources i found, for 2- valued truth-functional implication. What I'm saying is that implication-propositions don't translate to logical "IF-THEN" statements that are used by people and computers via their programming. As for people: That was the whole point of the story, ...to illustrate that the standard truth table for such implications can give results that differ from what people ordinarily expect. And no, i''m not "moving the goalpost". It's something that I've been saying from the start. As for computer programs: Of course. So what? A computer program doesn't interpret an "IF...THEN" statement as a logical proposition that a conclusion follows from a premise. It takes it as an instruction to do something if a certain proposition t is true. Loosely said, it often takes it as an instruction to make a variable take a certain value if a certain equality, inequality, or proposition is true. ... when the action called for is the execution of an assignment-statement. ...but it can also just specify an action, such as "IF x = a, THEN PRINT(x)" In general, it's an instruction, like saying, "If he tries to get in, call the police". Michael Ossipoff. • 1.2k A familiar difference between definitions in logic and human language, is the meaning of "or". As you may know, in logic, "A OR B" means "A", "B" or "A and B". If you just want one of them, you must use exclusive OR, abbreviated xOR. In human language it's the opposite. If the carnival game operator tells you that you've won a stuffed bear or a parasol, and you take both, you're obviously in the wrong. If you want inclusive OR, you have to say "A or B or both". Or, more briefly, A &/or B". No one is claiming that words always mean the same in logic and in human language. Michael Ossipoff • 1.2k That was the whole point of the story, ...to illustrate that the standard truth table for such implications can give results that differ from what people ordinarily expect. No. The point is that you can know a language, but translating the meaning to another can give results that differ from what people ordinarily expect when you don't translate it correctly. A computer program doesn't interpret an "IF...THEN" statement as a logical proposition that a conclusion follows from a premise. It takes it as an instruction to do something if a certain proposition t is true. Loosely said, it often takes it as an instruction to make a variable take a certain value if a certain equality, inequality, or proposition is true. ... when the action called for is the execution of an assignment-statement. ...but it can also just specify an action, such as "IF x = a, THEN PRINT(x)" Exactly. The sign is written as an IF-THEN statement. IF you give the clerk$5000, THEN you receive the diamond. IF-THEN-(ELSE) is how we make ANY decision.

You simply need to rewrite the sign so that it actually translates correctly - meaning that you need to remove the IF and the THEN and write it as two indpendent statements.

You still haven't given us the relationship between giving the clerk $5000 and receiving the diamond. Is it a causal relationship, or what? What does the arrow between p and q actually mean? No one is claiming that words always mean the same in logic and in human language. Human language is logical. • 1.2k Must quit for the evening. Replying tomorrow. Michael Ossipoff • 1.2k I’d said: . That was the whole point of the story, ...to illustrate that the standard truth table for such implications can give results that differ from what people ordinarily expect. . You replied: . No. The point is that you can know a language, but translating the meaning to another can give results that differ from what people ordinarily expect when you don't translate it correctly. . Incorrect. As the person who posted my post, I’m the one to say what my point was, in posting it. . Re-quoting you: . …you can know a language, but translating the meaning to another can give results that differ from what people ordinarily expect when you don't translate it correctly. . The truth-table that I (and others) quoted wasn’t complicated. It’s unambiguously expressed in English. No, there was no mis-translation of it in my story. . I’d said: . A computer program doesn't interpret an "IF...THEN" statement as a logical proposition that a conclusion follows from a premise. . It takes it as an instruction to do something if a certain proposition t is true. . Loosely said, it often takes it as an instruction to make a variable take a certain value if a certain equality, inequality, or proposition is true. ... when the action called for is the execution of an assignment-statement. . ...but it can also just specify an action, such as "IF x = a, THEN PRINT(x)" . You replied: . Exactly. The sign is written as an IF-THEN statement. IF you give the clerk$5000, THEN you receive the diamond. IF-THEN-(ELSE) is how we make ANY decision.
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One point that I was making was that a computer language’s IF…THEN statement isn’t the same thing as a logical implication-proposition (…in this case one that’s interpreted in the standard manner of 2-valued truth-functional logic).
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At no time did the clerk tell the customer that the sign was a computer-language statement that was going to be executed after the payment. The clerk merely (correctly) stated the truth-value of the implication-proposition, by the standard 2-valued truth-functional interpretation, at a time before payment was made.
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No mis-translation. No lie.
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You simply need to rewrite the sign so that it actually translates correctly.
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As I said above, there was no mis-translation.
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You still haven't given us the relationship between giving the clerk \$5000 and receiving the diamond. Is it a causal relationship, or what? What does the arrow between p and q actually mean?
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It’s called an “implication-proposition”. Depending on what kind of logic one is referring to, there can be various truth-tables for it. In the standard 2-valued truth-functional interpretation, an implication-proposition is true if its premise is false.
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I’d said:
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No one is claiming that words always mean the same in logic and in human language.
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You replied:
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Human language is logical.
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:D
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Well, some languages are more logical than others.
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If you like language to be logical, then I recommend Esperanto. It’s more logical than English, and more logical than at least nearly all natural languages.
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Harry, this conversation has, for some time now, consisted only of repetition. It’s time for us to agree to disagree.
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I’m at these forums to discuss metaphysics.
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Michael Ossipoff
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This reply is just one giant circular argument.

In the link that Michael provided on the first page of this thread - and that you agreed with - also explains exactly what it was I've been trying to tell you for several posts now. If you scroll down to the section, "Philosophical problems with material conditional", it explains how the implications aren't completely translatable to a native language.

Outside of mathematics, it is a matter of some controversy as to whether the truth function for material implication provides an adequate treatment of conditional statements in a natural language such as English, i.e., indicative conditionals and counterfactual conditionals. An indicative conditional is a sentence in the indicative mood with a conditional clause attached. A counterfactual conditional is a false-to-fact sentence in the subjunctive mood. That is to say, critics argue that in some non-mathematical cases, the truth value of a compound statement, "if p then q", is not adequately determined by the truth values of p and q. Examples of non-truth-functional statements include: "q because p", "p before q" and "it is possible that p" — Wikipedia

It is not surprising that a rigorously defined truth-functional operator does not correspond exactly to all notions of implication or otherwise expressed by 'if ... then ...' sentences in natural languages. For an overview of some of the various analyses, formal and informal, of conditionals, see the "References" section below. Relevance logic attempts to capture these alternate concepts of implication that material implication glosses over. — Wikipedia

Relevance logic, also called relevant logic, is a kind of non-classical logic requiring the antecedent and consequent of implications to be relevantly related. — Wikipedia

Your "research" seems to be cherry-picked.
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The difference in meanings and interpretations described in your quote was what my story was intended to illustrate. As I said, that was the whole point of the story.

Your "research" seems to be cherry-picked.

Actually no, the standard 2-valued truth-functional implication truth-table was unanimously identical at every academic website that I checked.

But we've already been all over this several times.

Michael Ossipoff
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