This is such common knowledge about Logic, I thought Wiki would work. But at your request:
IEP: (emphasis added)
"According to the definition of a deductive argument (see the
Deduction and Induction), the author of a deductive argument always
intends that the premises provide the sort of justification for the conclusion whereby
if the premises are true, the conclusion is guaranteed to be true as well. Loosely speaking, if the author's process of reasoning is a good one, if the premises actually do provide this sort of justification for the conclusion, then the argument is
valid.
In effect,
an argument is valid if the truth of the premises logically guarantees the truth of the conclusion. The following argument is valid, because it is impossible for the premises to be true and the conclusion to nevertheless be false:
Either Elizabeth owns a Honda or she owns a Saturn.
Elizabeth does not own a Honda.
Therefore, Elizabeth owns a Saturn.
It is important to stress that the premises of an argument do not have actually to be true in order for the argument to be valid. An argument is valid if the premises and conclusion are related to each other in the right way so that if the premises were true, then the conclusion would have to be true as well. We can recognize in the above case that even if one of the premises is actually
false, that if they
had been true the conclusion
would have been true as well. Consider, then an argument such as the following:
All toasters are items made of gold.
All items made of gold are time-travel devices.
Therefore, all toasters are time-travel devices.
Obviously, the premises in this argument are not true. It may be hard to imagine these premises being true, but it is not hard to see that if they were true, their truth would logically guarantee the conclusion's truth...
Whether or not the premises of an argument are true depends on their specific content. However, according to the dominant understanding among logicians, the validity or invalidity of an argument is determined entirely by its logical form. The logical form of an argument is that which remains of it when one abstracts away from the specific content of the premises and the conclusion, i.e., words naming things, their properties and relations, leaving only those elements that are common to discourse and reasoning about any subject matter, i.e., words such as "all", "and", "not", "some", etc. One can represent the logical form of an argument by replacing the specific content words with letters used as place-holders or variables."
Validity and Soundness | Internet Encyclopedia of Philosophy
Also referred to as:
"Premises (
the ideas that argument is assuming to be true and advancing as evidence for the ultimate conclusion)"
Dr. Dona Warren Department of Philosophy The University of Wisconsin – Stevens Point
http://www4.uwsp.edu/philosophy/dwarren/whatisformallogic/whatisformallogicslides.pdf
Etc.... etc....
No it isn't. The problem isn't what physics is or isn't. The problem is asserting that one is begging the question by assuming as a premise that the laws of physics didn't conveniently change some 6000 years ago...
You seem to be unaware that all logical premises are assumptions... at least for the purposes of logic. If we can not accept as a fact any given assumptions at which to arrive at conclusions, than you and I can create entirely different valid arguments with radically different conclusions, because the premises from which the argument is made is not the same...
I didn't say you claimed the laws of physics weren't real. You are suggesting that it is impossible to know that the laws of physicians have been more consistent than over 200 years ago. Which is fine. But I'd wouldn't generally assume the same things to be true that you do. I acknowledge it's entirely possible that the laws of physics entirely changed 12 seconds ago, but I can't see it, because the new laws of physics only makes it look like stuff is much older than it is.
By the way, Newton wrote about "physics" 300 years ago. The majority of calculus is entirely legitimate. It didn't turn out to be wrong... it just didn't tell the whole story, nor explain everything that humans had seen in the universe or at a microscopic scale.
Talk about putting words in some one else's mouth. Personally I don't attend any place of worship, whether it's the worship of the scientific method for arriving at truth claims about the physical reality we exist in, or a fictitious entity written a book than no one has any more access to or proof of.
P1: The laws of physics are not subject to whimsical change or purposeful change from an outside agent.
P2: Radiometric dating is consistent if and only is the laws of physics are not subject to change.
P3: Radiometric dating of various forums show that the age of various rocks on the planet date back nearly 4 billion years.
Conclusion: The planet is nearly 4 billion years old.
I mean, if P1 is too much of an assumption for you, I can see why you think my argument is unsound. But it's not less valid whether or not P1 is true or not.