We have seen that the major sources of valid knowledge are perception (prathyaksham प्रत्यक्षं), inference (anumaanam अनुमानं), analogy (upamaanam उपमानं), and verbal testimony (shaabdam शाब्दं). Indian science has always been a humble approach of Man towards the peaceful co-existence with nature. This reflects in their ordering of the sources of knowledge too. Perception (prathyaksham प्रत्यक्षं) is the most natural of the three sources of knowledge. After all, what can be more natural than what you observe directly through your senses! So, the Indian logicians have placed prathyaksham above all the other sources of knowledge. Inference, which is the effort to derive knowledge from the observed facts, comes next only to pratyaksham in the framework of tarka shaastram. Knowledge from examples (analogy) is the next valid source of knowledge. The repository of knowledge accumulated over the ages (shaabdam शाब्दं or aagama आगम) is placed next to the knowledge from examples. In the following sections, we shall deal with Inference (anumaanam अनुमानं).

Let us begin with an example. A very common example that is dealt in the tarka framework is as follows:

One observes smoke in a mountain. The conclusion that one can make out of this observation is that the mountain is pervaded by fire. This is a simple case of inference (anumaanam अनुमानं). We shall try to understand it better. When we see smoke in the mountain, the following may come to our mind :

- There is smoke in the mountain.

- Smoke is always pervaded by fire. We've seen this in case of hearth, kerosene stove etc.

- So, if there is smoke somewhere, there should also be fire there.

- Hence, there is fire in the mountain.

In this example, we see that

- "Fire" is that which is to be proved.

- The reason for our conclusion of  the presence of  fire is "smoke".

- There is an indisputable association between smoke and fire i.e, wherever there is smoke, there is fire.

- Mountain is the current place where the above association exists.

In the parlance of tarka shaastram, the thing to be proved (fire) is called the saadhya (साध्य). The reason (smoke) is called the 'hetu' (हेतु). The association (between smoke and fire) is called vyaapti  (व्याप्ति). The place (mountain) where we suspect the presence of saadhya is called the paksha ( पक्ष).

You can see that, any case of inference similar to that discussed above, will contain the basic building blocks - paksha, saadhya, hetu, and vyaapti. Just to recap,

1. Paksha - The subject or the receptacle on which we formulate our deductions.

2. Hetu - Reason existing in the paksha

3. Saadhya - The thing we are trying to prove.

4. Vyaapti - Vyaapti is the quality of Saadhya being certainly co-existent with hetu in the same subject. This forms the central part of inference.

Inferential knowledge arises out of what is called as paraamarsha (परामर्श). Paraamarsha is nothing but the knowledge of hetu existing in the paksha accompanied by vyaapti (of saadhya). In our example of the mountain and smoke,  the knowledge "this mountain has smoke", accompanied by the vyaapti of 'fire being co-existent with smoke' is  paraamarsha. The knowledge - the mountain has fire -  that results from paraamarsha is the inferential knowledge (anumiti).