According to classical Indian school of logic (Nyaya) which fallacy is committed in the flowing argument Anything that is thinkable is nameable because it is thinkable.

The correct answer is Svarupasiddha.

In classical Indian logic (Nyāya), a fallacy of inference is known as a Hetvābhāsa (pseudo-reason). For an inference to be valid, the middle term (hetu or reason) must be present in the minor term (pakṣa or subject of inference). This condition is called pakṣadharmatā.

The fallacy of Siddha (unproved) or Asiddha occurs when the middle term is not proved to exist in the minor term. Svarūpāsiddha (nature-unproved) is a subtype of this fallacy which occurs when the middle term (hetu) cannot be present in the minor term (pakṣa) because its very nature (svarūpa) makes it impossible or untrue of the minor term.

In the given argument:
"Anything that is thinkable is nameable because it is thinkable."
Here, we are trying to establish the relation. However, let us examine the structure:
- Minor term (pakṣa/subject): "Anything that is thinkable" (which refers to all thinkable things, or the universe of thinkable objects).
- Major term (sādhya/predicate): "nameable".
- Middle term (hetu/reason): "because it is thinkable".

In Nyāya, the middle term (hetu) must exist in the minor term (pakṣa). But here, the minor term itself is "thinkable" (or everything that is thinkable), and the reason given is also "thinkable". Since the hetu (reason) cannot reside in itself in a way that provides a step of logical movement or because it fails the test of being a valid, distinct locus of proof for the subject, it is classified under the fallacy of Svarūpāsiddha where the state of the reason (hetu) in the subject (pakṣa) is unproved or unreal in its very nature.