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Validity and truth are independent in logic because formal logic systems are only as truthful as their axiomatic premises. When Sauron said in an earlier post that logicians and philosphers had declared that certain logical arguments concerning the existence of God were both valid and truthful he was wrong, since logic can never tell us anything about truth, independent of the assumed truth of axioms. The axioms of the real world are unknown so formal logic can never arrive at truth when describing the real world. In certain perfect domains such as planar geometry formal logic can arrive at truth, but only with respect to that perfect domain with its defined axioms.

The argument from first cause that Sauron expounds is a trivial linkage between assumptions and conclusions. Essentially Sauron supports a couple of assumptions that guarantee the conclusion, "A being created the universe", to wit, "1. The universe exists", "2. Everything that exists was created by a being". The moment you don't accept these presumptions as axioms (and many don't) the uncaused cause argument falls apart.

Doubtless all of this is covered in the logic primers that Sauron has been telling us about. When Sauron gets round to reading them he'll understand better.

Remarkable coincidence that XOR has been misunderstood twice in one week on FR crevo threads.

Well said. In addition, we should probably discuss what goes into a valid argument, as well as discussing the truth of an argument. Briefly, in deductive logic, a "valid" argument is one whose conclusion is a necessary consequence of the premises - that is, if the premises are true, then in a valid argument, the conclusion must necessarily be true as well. One does not have to accept the truth of the premises for an argument to be valid - one must merely recognize that if you accept the truth of the premises, the conclusion would be necessarily true as well.

For syllogistic arguments, validity is purely a formal matter - i.e., is the argument of a proper form? The argument I gave above, of the following form:

P1: All S is P.
P2: All P is Q.
C1: Therefore, all S is Q.

...is valid by its very nature. In the example above, the argument regarding cats and spines is valid as a matter of form, as well as being true. Of course, it's also perfectly possible to formulate valid arguments that are untrue:

P1: All cats are purple animals.
P2: All purple animals are dinosaurs.
C1: Therefore, all cats are dinosaurs.

This argument is of precisely the same form as before. If the premises of such an argument are true, then the conclusion must necessarily be true as a consequence - therefore, this argument is valid. However, we know the premises to be untrue, and therefore the truth of the conclusion is logically suspect as well.

Similarly, it is quite possible to formulate an argument that is invalid, and yet still true. The fallacy of the fourth term is a common occurrence:

P1: All cats are furry animals.
P2: All furry animals are mammals.
C1: Therefore, humans are mammals.

This is a sterling example of an argument which has entirely true premises, and a true conclusion, but is logically invalid in that the conclusion, even though true, does not follow from the premises - it is not a necessary consequence of the stated premises.

Finally, it is also possible to have an argument that is both invalid and untrue:

P1: All evolutionists support Darwin's theory.
P2: All Nazis support Darwin's theory.
C1: Therefore, all evolutionists are Nazis.

Needless to say, minor variants of this argument are not exactly unknown in these parts. Nevertheless, the conclusion is patently false. Spotting the fallacy that renders this argument invalid is left as an exercise for the reader.