Prabhupāda: . . . he is speaking about knowledge, perfect knowledge. Knowledge received from common man or any person within this material world, infected with four kinds of defects, cannot be perfect. The so-called scientists, philosophers, mental speculators or dramatists or writers, as we experience, their talkings all are nonsense—this is our challenge—because the basic principle of their knowledge is ignorance, ajñāna. Big, big scientists, they simply theorize, and they try to support their theories with the words, "It may be," "perhaps."
That is not perfect knowledge. As soon as you say: "It may be," that means you have no perfect knowledge. As soon as you say "perhaps," that means you have no perfect knowledge. So all these scientists and philosophers—they use these words, "it may be," "perhaps." Therefore we have to receive knowledge from a perfect person.
A perfect person means who is not illusioned, who does not commit mistakes. All of us, we commit mistakes, but a perfect person does not commit mistakes. This is the difference between perfect and imperfect. We are illusioned to accept something in place of something else. Just like the example is given by some philosophers to accept the rope by mistake as a snake. This is called illusion. To vision water in the desert, this is due to our imperfection. So a person who is liberated, or not under the control of the material nature, he is not illusioned, neither he commits mistakes. Another defect is our senses are imperfect.