For there to be any knowledge at all, there has to be ideology inthis sense; there has to be some preexisting agreement concerningwhat will countas knowledge, or what criteria will be used to judgenew or developing knowledges. In this second sense, ideology is adescriptive(rather than prescriptive) word, attempting to show theway things are, a whole way of life in a social group.
This paragraph reminds me a lot on the concept of post truth. No one can form what they believe as true without there already being a pre-existing knowledge/truth before it. We then use that knowledge to develop what we believe to be true.