Verdade e Validade
Autor: No espaço dos conceitos | Publicado: 2011-07-22T18:26:00-07:00

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 <![endif]-->  Uma das questões mais cômicas e engraçadas para os alunos na aula de lógica é a respeito da questão da validade e da verdade. Pois, podemos observar diversos casos em que o argumento pode ser inteiramente válido e não verdadeiro. Vejamos o seguinte exemplo:
&nbsp;Todo extraterrestre tem duas pernas&nbsp;Luis tem duas pernas;&nbsp;Logo, Luiz é extraterrestre.
Este argumento é inteiramente válido, temos duas premissas e uma conclusão perfeitamente válidas. Isso não quer dizer que o argumento seja verdadeiro. O fato de todos os extraterrestres terem duas pernas não transforma todos os bípedes em extraterrestres. A validade não está ligada neste caso a verdade. Vejamos um exemplo clássico da lógica onde o argumento é válido e verdadeiro. Aonde temos duas premissas válidas e uma conclusão também válida:
Todo homem é mortal;Sócrates é homem;Logo, Sócrates é mortal.
Vemos que o argumento oferece uma informação que observamos no cotidiano. Como também apresenta um conteúdo. &nbsp;Até agora não observamos um ser humano imortal. No caso da validade não devemos observar ou olhar o conteúdo. A validade depende da forma do argumento.