Logic is a method of argument in which we check for consistency. A lot of people do not understand the difference between “logic” and “truth”. Logic is a test of consistency. “Relative truth” is a true statement which is dependent on certain conditions. “Absolute truth” is a true statement that is independent of any form of dependency to conditions.
In science, all truths are “relative”. For example, when we say that water boils at 100 degrees Celcius, its not an absolute truth because it depends on conditions such as pressure equal a specific value. I mean on the top of the Himalayas, water boils at less than 100 degrees Celcius …closer to about 60 -70 degrees Celcius due to the “lower atmospheric” pressure there. Truths in science are all relative because they are either dependent upon “observations” or “experiments” to “prove them”. In other words, “observations” & “experiments” give “results” that are “true” with “respect to” the “conditions in which they are observed or performed”. A “change” in these conditions or factors that effect these phenomenons will result in a “variation” of the “observation or experiment”. No one can 100% say a phenomenon will happen the same way in a “different state” elsewhere in the Universe. This is what Einstein came to put forth in his theory of relativity. He even suggested that time is relative… lets not get to far into the discussion of dimensions and time. If science was an absolute truth, then we MUST be able to “deduce” with just a pen and paper & an “idea” all the results in science. Since this is not true, thus science is not an absolute truth as many believe so. The truths in science are all depended on earlier results or physical or whatever else conditions.
Is there “absolute truth”? Yes, for example Mathematics. Indeed mathematics is the ONLY knowledge in human civilization that boasts the unique feature of being an absolute truth in “itself”. This is because with just a pen, paper & an “idea”, one can deduce all truths in mathematics. It does NOT depend on “experiments” or “tests” or “guesses”. Its statements can be proven with sound reasoning. One may also argue to say that mathematics is not really an absolute truth in an “absolute sense” because its statements all can be traced to a “primitive set of assumptions” called “axioms”. Axioms are NOT provable and are “pre determined/set” as “conditions” using which one can build a theory in mathematics from it. So, maths is a “absolute truth in itself” but not in the arbitrarily “absolute sense” because it still depends on “building blocks of ideas called axioms” whose “truth” is just “pre set”. Different “axioms” thus give birth to different branches of mathematics for example, Euclidean geometry versus non Euclidean geometry. When to apply “which” mathematics? The answer is simple : Just use the filed of mathematics to a situation to deduce equivalent results after checking that the axiomatic assumptions of the “branch of mathematics in concern” is satisfied to the “scenario” in which we wish to apply it. I believe the only absolute truth is “God”, its not dependent on “proof” nor a “disproof”. That’s a different discussion…
Based on a set of “assumptions” logic is used to “deduce” as well as “check” whether or not the “claims” we make are compatible and does not contradict our “initial assumptions”. The “initial assumptions” are given the name “premises” or “hypothesis”.