This life we live has one main impurity of perception in its present condition. This is called ajnana or not jnana or not total knowledge. Partial knowledge is the manufacturing defect we are born with.
There are many synonyms for this word and one of them is avidya. In the Brahma Sutra commentary, Adi Sankaracharya points out that it is adhyasa or unconscious superimposition. He says it takes the form of memory. In another place and on another object, placing what we have already seen, heard or experienced is adhyasa.
This adhyasa is an instantaneous misapprehension due to non-apprehension of the substratum.There are many common examples to explain this in Vedantic language. One is of the snake and the rope, and another is the silver and the shell on the beach. In a dark garden pathway, there lay a thick rope. The person who brought it, forgot and left it lying. Someone who did not know this was walking on the path and darkness had set in. He set foot on the rope and shouted out of fear. People came running to help him and he was shivering with fear. All their consolation was of no avail until someone brought a torch and made the quaking man touch the object and take it in his hand to ensure it was a rope.
You are taking a walk on the beach in broad daylight. A child is coming along with you and sees many bright pieces shining in the sand. She runs to pick it up thinking it is silver. When she goes close, she realises it is just a shell which appeared like silver reflecting the sunlight. In the two instances, what caused the misperception is a natural error in our understanding called avidya. It is an impurity of mind that is the breeding ground for other impurities such as ego, attachment, hatred, fear, selfishness, arrogance and jealousy.
The Acharya talks of ajnana as an impurity. He means superimposing eternity on our experiences and hoping to attain heaven, superimposing cleanliness and calling the body ‘I’ when it is indeed a packed assemblage of unhygienic biodegradable waste material. We go after objects such as fragrances and pleasures which actually contain sorrow in it.
The Atma Bodha says that the ajnana can be removed by practice of right knowledge. Having accomplished the task of removing ignorance, the knowledge also disappears like the kataka nuts which are dropped in water. They clean up the water by absorbing the dirt and in the end, the water is decanted and freed of the nuts too.