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/illumination; 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, without any 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 with which different object-aspects are apprehended, and in the differing clarity with which object-aspects are apprehended under different conditions and circumstances.

The mental factor of wisdom operates in parallel and in mixture 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, its discernment of the corresponding object-aspect becomes unclear, and it cannot make a correct, reasonable, and truthful decision, nor can it make a decision promptly—the outcome can well be imagined. The mental factor of wisdom functions at every stage of the operation of the five universally active mental factors, and it must also function in the operation of the other five object-specific mental factors; otherwise the conscious mind becomes disordered and cannot make truthful and reasonable decisions.

Take, for example, the operation of the eye consciousness: at the very beginning, the eye consciousness's own mental engagement (manaskāra) and contact (sparśa) may not involve the participation of the mental factor of wisdom, but as the operation proceeds further, the mental factor of wisdom becomes involved. When the 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 regarding 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—one sinks deep into worldly saṃsāra without realizing it.

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