Consciousness is a property of the soul, but not an essential property. Consciousness cannot exist without the soul, but the soul can exist without being conscious. The earliest Nyaya philosophers held what must be the oddest doctrine of liberation ever taught. Their investigations led them to conclude that the essence of liberation is freedom from pain and suffering. Some describe liberation in terms of delight and bliss, but the Nyaya points out that nothing can counts as liberation unless it includes the permanent extinction of pain and suffering, and that, therefore, it is this that must be the essence of liberation.
Liberation is the final extinction of all pain and suffering.
This is attained not merely by the acquisition of appropriate philosophical knowledge. Liberation takes place when all effort, activity, all consequences of activity, all tendency to incarnation, and all association with a body come to an end, and therefore all consciousness. No consciousness says the older Nyaya, no pain. Not surprisingly this purely negative theory attracted little support, and over the centuries it seems to have faded away. There is a problem in interpreting this sutra, since it is not at all clear who is to be presumed to say it.