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The assertion that a statement is a "necessary and sufficient" condition of another means that the former statement is true if and only if the latter is true. That is, the two statements must be either simultaneously true, or simultaneously false. [4] [5] [6]
Broadly speaking, a logical truth is a statement which is true regardless of the truth or falsity of its constituent propositions. In other words, a logical truth is a statement which is not only true, but one which is true under all interpretations of its logical components (other than its logical constants).
It can be summarized as "P implies Q. P is true. Therefore, Q must also be true." Modus ponens is a mixed hypothetical syllogism and is closely related to another valid form of argument, modus tollens. Both have apparently similar but invalid forms: affirming the consequent and denying the antecedent.
We must not present a fact as an opinion, nor an opinion as a fact; and so on for the other categories. Besides, truth is a boolean value (100% true or 100% false) only in certain technical contexts, such as mathematics or programming languages. In most other contexts, there are more than truths and lies under the sun: there are half-truths ...
Unless it has previously been established that her outfit is a dress, the question is fallacious because she could be wearing pants instead. [ 28 ] [ 29 ] Another related fallacy is ignoratio elenchi or irrelevant conclusion : an argument that fails to address the issue in question, but appears to do so.
It is not required for a valid argument to have premises that are actually true, [2] but to have premises that, if they were true, would guarantee the truth of the argument's conclusion. Valid arguments must be clearly expressed by means of sentences called well-formed formulas (also called wffs or simply formulas ).
For a given fallacy, one must either characterize it by means of a deductive argumentation scheme, which rarely applies (the first prong of the fork), or one must relax definitions and add nuance to take the actual intent and context of the argument into account (the other prong of the fork). [27]
An early variety of deflationary theory is the redundancy theory of truth, so-called because—in examples like those above, e.g. "snow is white [is true]"—the concept of "truth" is redundant and need not have been articulated; that is, it is merely a word that is traditionally used in conversation or writing, generally for emphasis, but not ...