~ Pratyakshanumanagamah pramanani ~
So in this sutra, the rishi explains what is right knowledge. Right knowledge can be attain by three sources – sense evidence, inference and testimony. Sense evidence refers to knowledge by the contact of one of our sense organs. e.g. We see a rose, we smell a rose, we hear someone laughing, we touch an object that is hot or cold. Inference refers logic and reasoning, from a distance, we see smoke in the mountains, we can then use reasoning and know that there is fire in the mountains. Testimony is based on what other people say who provides you knowledge, however, there are two requirements -the person should impart the right knowledge and secondly, the person must impart that knowledge without any mistake. When these two conditions are fulfilled then we can take it as right knowledge. Scriptures are also considered as testimony as they are a collective revelations of rishis – ancient seers.
Reference ~ Four Chapters of Freedom by Swami Satyananda