Bacon's four idols are the tribe, the cave, the marketplace, and the theater. He asserts that each of these "idols" prevents men from attaining true understanding.
The idols of the tribe are basic to the human condition. The idols of the cave deal each individual person. The idols of the marketplace deal with society as a whole. The idols of the theater are scientific facts that are groundless because they have not been supported, but are generally accepted as the truth.
Bacon asserts that, in as far as the laws of nature are observed, the only way to truly become knowledgeable and understand the world comes through individual exploration, along with reason, and testing one's understandings to be sure they are accurate. Bacon's sense is that one does not take things on faith: the foundation for someone's "beliefs" come from reason and irrefutable evidence.