"Truth is a kind of error without which a particular kind of living creature could not live. The value for life is ultimately decisive." - Friedrich Nietzsche
T) Truth is the idea that our thoughts correspond with reality
A) Man (or any living creature capable of thought) needs an idea of "truth" - Creatures cannot hold an idea without having the "idea about something", i.e. existence has to be taken as a priori.
B) Truth may not be "real" - i.e. Things may not have truth value and they need not be absolute - since any investigation into the "truth" of something ends up in having to take certain things for granted, w/o knowing their truth value.
C) T + A + B: In absence of "truth", no basis for thought OR ideas cannot be validated via "reality checks"
Nietzsche) T + A + B: Assuming things are "true" leads to false assumptions of existence. Hence the concept of truth is a wrongly held belief. + C: validation of ideas (a process required to decide about the correctness of any object - whether psychological/mental or material) is done by evaluating the "Value for Life" the creature holds (read selfishness). Nietzsche's target "ideas" was (sic) Morality
Arguments in Support
Skepticism) B cannot be disproved, since the process of finding the truth about something inherently demands acceptance of things which may not be true.
Nihilism) C can imply that their is no reality Or at least Man's conception of reality is spurious. However, may also argue that the value for life is ill-founded and can be arbitrarily different for different people, thus may not lead one (or many) to a rational end.
Mysticism) Since C, therefore the mind fabricates reality. This implies that reality may not exist or also that one has no way of knowing what is real; hence any "grasp" of reality would be illusory and any decision taken on the basis of such a illusory basis would necessarily be in error. In such an ideological vacuum, decisions can be taken on any arbitrary basis and that is what Man does. The preferred basis could be derived from divinity or self-interest.
Pragmatism) B implies that it is not always useful to investigate the Truth. "Value for Life" is a practical way to decide about things. (read: moral judgments)
Arguments in Opposition
Realism) B is false. Reality exists regardless of your wishes or knowledge of it. Thus A is the only way to "know" and think about something and hence the only way to live. If not then you could live in your hypothetical/imaginary world and your desires (arbitrary sense of Value for Life) could bear out to be "real" / applicable. This doesn't happen.
Rationalism / Empiricism / Representational-ism) Variants of Realism: Truth can be observed by trusting the senses or finding the logic to necessitate the existence of it. In effect whatever we conceptualize after a reasonable investigation is "The Truth".C would imply a negation/denial of our own existence.
Objectivism / Naturalism) Goes further from the above to claim that reality cannot be other than what is observed and perceived by us and to claim that Truth may not exist is a "criminal" error as it would completely nullify Man's faculty for thinking and render Man impotent, thereby creating severe impediment in realizing the Value for Life. It maintains that "Value for Life" cannot be contradictory with Truth (or reality) and thus would be equally (or rather synonymous-ly) decisive about moral judgments.
I adhere to the last point of view