Относно понятията за необходимо и достатъчно условие
On the Concepts of Necessary Condition and Sufficient Condition

Summary/Abstract: The subject of the text is the logical analysis of the concepts of necessary condition and sufficient condition. Three explanations of what they mean are considered. The first, the material implication account, has the absurd consequence that if two sentences are true, the states of affairs they express are necessary and sufficient conditions for one another. In addition, it contradicts the way the concepts are used in mathematics, where a necessary or sufficient condition is given through a predicate rather than a sentence. The second explanation, the strict implication account, does not have the first of the above two deficiencies but has the key disadvantage that it is not applicable to the extensional language of mathematics, where the two expressions are most commonly used. The article defends an explanation through a formal implication. Unlike the other two, the formal implication account corresponds to mathematical usage. Moreover, when the necessary or sufficient condition is given through a sentence instead of a predicate, the account treats it as an intentional (modal) expression, which avoids the absurd consequence of the first account.

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