有效性

Multi tool use
提示:本条目的主题不是
效度。
在逻辑中,如果一个论证不能从真前提中得出假结论,则论证的形式是完全有效的。一个论证若被称为是有效的,则如果在其中所有前提都为真的每个模型中,结论也是真的。例如:“所有A是B;有些A是C;所以有些B是C”是有效形式。
- 一个逻辑公式被称为是有效的,如果它在所有释义(也叫做结构或模型)下都是真的。参见模型论或数理逻辑。
- 一个重言式,或重言公式,是真值泛函有效的。不是所有量化逻辑的有效的公式都是重言式。参见真值表。
例子
考虑下列论证形式,其中P、Q和A表示未分析的或未解释的句子。
- 所有P是Q,
- A是P,
- 所以A是Q。
实际论证的有效性可以通过把它转换到一个论证形式中,并接着分析这个论证形式的有效性来确定。(上述论证形式是有效的,参见三段论。)
- 如果所有P是Q,并且A是P,那么A是Q。
参见
 | 查询維基詞典中的有效性。 |
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