Vimarsha is a kind of discussion or thinking which takes place in one’s own mind, or even among the members of a harmonious team, either due to some samasya (doubt) or need of uha (reasoning) to understand the yet unknown cause of some new fact, or to nirnaya (decide) the right alternative out of two mutually opposite possibilities or objects of choice. The discussions take place among persons who are interested in presenting their own point of view or aspect noticed by them of the object under consideration. It remains for the organizer to draw any conclusion; vimarsha can be done by an individual also, taking the different aspects or alternatives into consideration to reach a conclusion.
In Nyaya philosophy, vimarsha is necessary in case of samasya (doubt), tarka (logic) and nirnaya (decision).
When two objects have some common features (samana dharma), a doubt arises whether the object before us is this or that. For example, a person is shown a multi-colored landscape picture or painting in which the sun is shown in reddish orange color just above the horizon. The person wonders whether the view is of sunrise or sunset. Now to remove this doubt and to have a correct identification of the view, some specific feature or characteristic of either sunrise or sunset should be known. The thinking on the samanadharma (common attributes) is vimarsha (samanadharmopapatter-viseshapeksho vimarsha samasya iti – Nyaya Bhashya on yayasutra I/1/23). It is thought-process and defines samsaya (doubt) in the sense described above. In case of common attributes, requirement of specification may also arise when no evidence is available either to prove or disprove an idea.
The second context is of logic (tarka). When an unknown object or fact or idea comes before someone, the person begins to think about it and its cause. The consideration of possibilities or alternatives and their evaluation is called vimarsha, as Vyasa puts it in Nyaya Bhashya (Nyayasutra I/1/40) – Jijnasitasya vastuno vyahatan dharman vibhagena vimarsati kim svid ittham ahosvinnetthamiti). Thus, after proper evaluation of the two sides, the person selects the acceptable and gives up the impossible. This whole process is logic, and vimarsha is its important part.
The third context of vimarsha is nirnaya (decision). To make a decision one has to examine the credibility of mutually opposite claims (paksha or thesis and pratipaksha or antithesis) as pointed out in Nyayasutra – Vimarshya paksha-pratipaksha-bhyamartha-vadharanam nirnayah (I/1/41). This critical examination of the opposites is vimarsha. After vimarsha, whichever claimant proves to be true, the decision goes in favor of that. Such vimarsha paves the way of Nyaya (Soyam vimarsah paksha – pratipaksavadyotya Nyayam pravartayati – Nyaya Bhashya on sutra I/1/41).
There is no place for vimarsha in direct perception (pratyaksha pramana) where the object of perception is self-evident or in case of sabda pramana (authentic word) which is believed as such, or also in case of vada (argument) where the debaters stick firmly to their position, whether right or wrong.