All members of this forum lie
I lie
therefore........?

for the record, Im not calling the forum-members for liars.

My only problem with it is that your conclusion is false.

A fallacious argument is an argument that contains an error. Some errors are so common that we actually name them. The most common error that I have seen is an error is reasoning. It's so common that I wouldn't find it unreasonable to characterize most fallacious arguments as arguments that contain an error in reasoning. The best medicine to cure such an ailment is to think. Think through what we, and others, are saying. Be thorough and methodical in our thought processes. Ask ourselves, does the conclusion really follow from the premises that are given in support of it?

By fallacious I'm assuming you mean unsound.

In which case, an invalid argument is one which is not in proper logical form. An argument such as:

All Italians are Europeans.
All Romans are Europeans

Therefore, all Romans are Italians.

Is not in proper logical form, because the middle term of the argument (Europeans) is not properly distributed. Therefore the above argument is not valid and therefore can not be sound. For an argument to be sound, it must have two true premises and be in valid form. For an argument to be valid, it simply must adhere to the proper form of an argument.

An argument, however, can be valid, and still be unsound, since a valid argument may have at least one false premise. There is also the problem that an argument that begs the question, or an argument that is circular, may be an argument that is valid and has all true premises. Yet, begging the question, and circularity, are fallacies.

Right, however, an argument cannot be sound unless it is valid, I think a sound argument is what laymen merely consider a good argument. Validity has noting to do with truth value, and fallacies are merely different categories of invalid arguments. The art of discourse is a lost art as even in political debates fallacies can be often found.

For an argument to be sound, it must have two true premises and be in valid form. For an argument to be valid, it simply must adhere to the proper form of an argument.

Two?

..................

Of course it depends on the Logical rules in which you are working under. I guess some would consider enthymemes valid arguments even if they are missing a premise. Also if you are working with sequential or predicate Logic, unlimited premises could be needed. In typical categorical syllogism, such as in the example I gave previously, two premises are the standard form. Even sorites must be broken down into standard two premise form to be tested for validity.

Yes you are correct Ken, fallacies can be valid, my mistake.

How about the argument, 1. No dogs are snakes. Therefore, 2. No snakes are dogs. One premise. One conclusion. And a sound argument.

That isn't a categorical argument. That is merely a conversion of one premise to another. Anytime you converse,obverse, or contrapose a premise, it will always be as true as the original premise, but that doesn't mean it is a conclusion. Nothing is being implied in the "conclusion" that isn't already evident in the first premise. Arguments are an attempt come to an understanding discursively, which requires putting premises together.

I don't know what you mean by a "categorical argument". An argument consists of at least two statements. One of which is the conclusion. The other of which is the premise. And the premise is supposed to support the conclusion. Nowhere does the definition say how many premises there must be. I think you are thinking of the argument called, the syllogism. Now, a syllogism is defined as an argument with two premises and a conclusion. But a syllogism is, of course, only one kind of argument. Of course, in every valid deductive argument, there is nothing in the conclusion that is not already in the premises.

By the way, the converse of All apples are fruit is, All fruit are apples. And, of course, those two statements are not equivalent. In fact, the first is true, but the second is false. You are talking about what are called "immediate inferences". And, immediate inferences are arguments with just one premise. There is no second premise to mediate between the premise and the conclusion. Syllogisms are called "mediate inferences" for the opposite reason. Obversion and contraposition are both immediate inferences.

Which is why I made the point that different forms of Logic have different rules. Aristotle developed categorical logic with the use of the syllogism. You can't just converse any statement you wish, immediate inferences only produce equivalences when done to certain types of statements. To get an equivalent statement, conversion must be done to a universal negative or a particular affirmative statement. Other types of immediate inferences also have similar rules, however, an obversion can be done on any type of statement.

What you presented :
1. No dogs are snakes. Therefore, 2. No snakes are dogs

is not an syllogism in categorical logic. It is an immediate inference of a statement.

The reason I am speaking in terms of syllogisms is because that was the initial type of Logic which you proposed earlier with the argument:

All Italians are Europeans.
All Romans are Europeans

Therefore, all Romans are Italians.

This argument is a syllogism, so it must adhere to the rules of categorical logic. It must have three terms, the middle term must be distributed at least once, and a term must be distributed in the premises if it is distributed in the conclusion.


If you wish to discuss a different form of Logic we could do that, but by presenting this argument in the form of a syllogism, I assumed that was the Logic in which you were referring to.

How are immediate inferences a different form of logic? Syllogisms and immediate inferences both employ categorical statements. Notice that the reason that All apples are fruit, therefore all fruit are apples, is not a valid argument is that the term "fruit" is undistributed in the premise, but not distributed in the conclusion. Thus it violated the rule that in a valid argument, a term undistributed in the premise cannot be distributed in the conclusion. Thus, it adheres to the same rule of logic as the syllogism. There is no difference except that immediate inferences have just one premise, but syllogisms have two premises. But the rules are exactly the same.

I never intended to convey immediate inferences were a different form of Logic from anything. What I said was that different inferences work on different forms of statements. Validity and Soundness both work the same for all arguments, yet all inferences are not possible on all forms of statements.

Where do we disagree? You agree, don't you, that all fruit are apples can be false, even if all apples are fruit is true? That means that the former statement does not follow from the latter statement. Isn't that right? So, we must be saying that the argument 1. All apples are fruit, therefore, all fruit are apples, is an invalid argument. So, what is your objection?

I don't think we disagree so much, as we are just coming closer to an understanding.

I am agreeing that the inference: 1. All apples are fruit, therefore, all fruit are apples, is invalid, and I was trying to explain why it was invalid.

Different types of inferences are only possible on certain statements, and I wasn't sure if you understood that concept, but now I see that you might have.