The Operation and Function of the Mental Factor of Wisdom (prajñā-caitta)

All eight consciousnesses possess the mental factor of wisdom (prajñā). Wisdom is clarity; without wisdom there is ignorance (avidyā). The mental factor of wisdom indicates the degree to which the conscious mind clearly apprehends the object-aspect it takes as its object. Of course, this clarity varies in degree. Only the eighth consciousness completely and thoroughly apprehends its object-aspect, with no ignorance. The other seven consciousnesses apprehend their object-aspects with varying degrees of clarity—not fully clear, still containing ignorance, and moreover with ignorance exceeding clarity. The degree of clarity is manifested in the differing clarity toward different object-aspects, and in the differing clarity toward the same object-aspect under different conditions and circumstances.

The mental factor of wisdom operates in parallel and mixed together with the other mental factors, inseparable from them. If the mental factor of wisdom fails to function while the conscious mind is operating, the mind's operation becomes disordered, and the corresponding object-aspect is not clearly discerned. Then one cannot make a correct, reasonable, and truthful decision, nor can one make a decision promptly—the consequences can well be imagined. The mental factor of wisdom functions at every stage of the operation of the five universal mental factors, and it must also function in the operation of the other particular mental factors; otherwise the mind becomes disordered and unable to make truthful and reasonable decisions.

Take the operation of eye consciousness, for example. At the very beginning, eye consciousness's own mental engagement (manaskāra) and contact (sparśa) may not involve the mental factor of wisdom, but as the operation proceeds further, the mental factor of wisdom becomes involved. When eye consciousness receives the material sense-object, the mental factor of wisdom functions, and one knows what the form is. Afterwards, when grasping the material sense-object, the mental factor of wisdom functions; and when making decisions about the material sense-object, the mental factor of wisdom functions even more. The stronger the mental factor of wisdom, the wiser the decision and the more wholesome the result. The same applies to the other consciousnesses; especially in the operation of the sixth and seventh consciousnesses, the force of the mental factor of wisdom is greater and the wisdom stronger. However, this wisdom is divided into worldly wisdom and the wisdom of the Buddha's teachings. Worldly wisdom is in fact also ignorance, not true clarity; it cannot lead to liberation and the attainment of Buddhahood, and may even do the opposite—sinking deep into worldly saṃsāra without realizing it.

In the operation of the particular mental factors, the mental factor of wisdom also operates simultaneously alongside them. The mental factor of wisdom operates in conjunction with the mental factor of desire (chanda), in conjunction with the mental factor of determination (adhimokṣa), in conjunction with the mental factor of mindfulness (smṛti), and in conjunction with the mental factor of meditative concentration (samādhi). But the power of wisdom in the mental factor of wisdom varies in strength, and its effects differ in magnitude, so the results differ enormously.