Gautama, the founder of the Nyāya school of Indian philosophy, provides a rigorous and influential definition of Pratyaksha (Perception) as a valid means of knowledge (pramāṇa). His definition is encapsulated in the sūtra: "Indriyārtha-sannikarṣotpannaṃ jñānaṃ avyapadeśyam avyabhicāri vyavasāyātmakaṃ pratyakṣam."

Let's break down the key elements:

1. Indriyārtha-sannikarṣotpannam (Arising from Sense-Object Contact): This is the fundamental condition. Perception arises directly from the immediate interaction between a sense organ (e.g., eye, ear) and its appropriate object (e.g., color, sound). Without this direct contact, there is no perception. This emphasizes the empirical and immediate nature of perception.

2. Avyapadeśyam (Non-verbal/Indeterminate): This refers to the initial, pre-linguistic, or Nirvikalpaka Pratyaksha (Indeterminate Perception). At this stage, the mind grasps the object's bare existence and its general features without any conceptualization, naming, or categorization. It's a pure, unanalyzed apprehension, like seeing a color without identifying it as "blue."

3. Avyabhicāri (Non-erroneous/Infallible): Perception, to be valid, must be free from error or illusion. It should accurately represent the object as it is, without distortion or contradiction. This excludes illusions (like seeing a snake where there is a rope) or dreams from being valid perceptions.

4. Vyavasāyātmakam (Determinate/Definite): This refers to Savikalpaka Pratyaksha (Determinate Perception). This is the stage where the initial indeterminate perception becomes conceptualized, categorized, and verbally expressible. Here, the object is recognized, identified with a name, and understood in relation to other objects (e.g., "This is a blue pot"). While subsequent to Nirvikalpaka, it is still considered perceptual because it's built upon the direct sense-object contact.

Gautama's definition meticulously distinguishes valid, immediate, and direct knowledge from other forms of knowledge (like inference) and from erroneous cognitions, firmly establishing perception as the primary and most certain pramāṇa.