Samkhya Karika 33

अन्तःकरणं त्रिविधं दशधा बाह्यं त्रयस्य विषयाख्यम् ।
साम्प्रतकालं बाह्यं त्रिकालमाभ्यन्तरं करणम् ॥ ३३ ॥

antaḥkaraṇaṁ trividhaṁ daśadhā bāhyaṁ trayasya viṣayākhyam ।
sāmpratakālaṁ bāhyaṁ trikālamābhyantaraṁ karaṇam ॥ 33 ॥

antaḥkaraṇaṁ=inner instrument; trividhaṁ=three-fold; daśadhā=ten-fold; bāhyaṁ=external; trayasya=of the three; viṣayākhyam=known as objects (of the three); sāmpratakālaṁ=present time; bāhyaṁ=external; trikālam=operating in all three times; ābhyantaraṁ=internal; karaṇam=instrument

The inner instrument (the three internal organs) is three-fold. The external organs are tenfold and are the objects of the three. The external organs function only in the present whereas the internal organs operate in all three times (past, present and future).

antaḥkaraṇaṁ (inner instrument): The threefold inner instrument comprises the mind (manas), ahamkara (ego) and the buddhi (intellect). Another well-known definition of antaḥkaraṇaṁ comes from the Vedantic tradition wherein a fourth component – chitta (memory etc.) is also added to the three given in Samkhya. The chitta (not to be confused with the word “chitta” used by Patanjali in the Yoga Sutras) is a composite of pure memory (smriti), samskaras (impressions) and vasanas (subtle desires). In Samkhya, the memory is supposed to be associated with each of the three inner instruments.  

The ten-fold external organs are: five organs of sense perception (eyes, ears, nose, tongue, and skin) and five organs of action (speaking, walking, taking (holding), excretion, and procreation). All these ten are objects for the three internal organs. For example, when the eyes capture the visual image of an external object, the image is received by the mind which does the initial apprehension (saṁkalpa – karika 27). Ahamkara offers self-identification (abhimāna – karika 24). Buddhi does the final ascertainment as to what the object is and what action needs to be taken (adhyavasāya – karika 23).

The second part of the karika states that the external organs can function only in the present timeframe. For example, if I am looking at a mango, the eyes can only capture what is available in the present moment. They cannot capture how the mango was ten days ago or how it will appear ten days from now. On the other hand, the three internal organs can function in all the three times – past, present, and future. Because of our past experience, the internal organs can access the memory and determine what the mango might have looked like ten days ago or how it might look in the future. As we have seen earlier, one of the three forms of correct cognition (Pramana) is anumana (inference). When we see muddy water in the river (present), we infer that it must have rained some time ago (past). Similarly, by looking at dark, dense clouds (present), we can infer that rainfall is imminent (future).