====== Intensional fallacy ======

Terms that can be used as synonyms in their extensional sense are used in ways that associate them with ambiguous intensions.

For example:

> The terms "morning star" and "evening star" both refer to the planet Venus.
> The //morning star// can be seen in the //morning//.
> <s invalid conclusio>Therefore, the //evening star// can also be seen in the //morning//.</s>

Even though the two terms have the same [[glossary:extension|extension]] (namely, the [[wp>Venus|planet Venus]]) and therefore can be used as [[glossary:synonym|synonyms]] in many situations, they carry specific secondary meanings ([[glossary:intension|intensions]]) because of the way they refer to it, thus making the above conclusion contradictory.

===== Other names =====

  * [[ambiguity:masked_man|“Masked man” fallacy]]
  * Illicit substitution of identicals

===== Description =====

The //intensional fallacy// belongs to the group of [[ambiguity:index|fallacies of ambiguity]], but is effectively the opposite of the other ambiguities here, which are all based on a term referring to more than one possible [[glossary:extension|extension]]. Here, there are multiple terms which refer to the same //extension// (i.e. they are [[glossary:synonym|synonyms]]), but in ways that imply different [[glossary:intension|intensions]], which can lead to invalid statements.

===== More examples =====
==== Intensions in the concept of God ====

> The Pope believes in God.
> The term "God" describes the same entity as "Allah".
> <s invalid conclusio>Therefore the the Pope believes in //Allah//.</s>

Although Christianity, Islam and Judaism, as a consequence of their common history and also according to their self-understanding refer to the same supreme deity, and although “<bdi :ar [style=font-size:120%]>الله</bdi>” [<i [dir=ltr] :ar-Latn>Allāh</i> ], as well as “<bdi :he>יהוה</bdi>” [<i :he-Latn [dir=ltr]>Jahwe</i> ] can also be understood as direct translations of the English word “God” (and are also used in such a way, under specific circumstances), the Arabic and Hebrew terms have specific //intensions// which stand in the way of a conclusion like the above. 

<aside info>
**Note:** This is with regards to the common use in English. In other languages, it may be different. For example, in [[wp>Maltese language|Maltese]] "<i :mt>alla</i>" is the proper translation for "God", also in a Catholic context.
</aside>

===== See also =====

  * [[glossary:equivocation:index|Equivocation]]
  * [[glossary:extension|Extension]]
  * [[glossary:intension|Intension]]
  * [[glossary:leibniz_law|Leibniz’ law (of the identity of indiscernibles)]]

===== More information =====

  * [[wp>Masked-man fallacy]] on //Wikipedia//
  * [[https://www.logicallyfallacious.com/logicalfallacies/Illicit-Substitution-of-Identicals|Illicit Substitution of Identicals]] on //Logically Fallacious//
  * [[https://www.fallacyfiles.org/illisubs.html|The Masked Man Fallacy]] on //Fallacy Files//