KNOWLEDGE being to be had only of visible and certain truth, ERROR is not a fault of our knowledge, but a mistake of our judgment giving assent to that which is not true.
 John Locke, An Essay Concerning Human Understanding (1689). copy citation

Context

“but would prove a very ill rule for men to choose their opinions or religion by. CHAPTER XIX. [not in early editions] CHAPTER XX. OF WRONG ASSENT, OR ERROR. 1. Causes of Error, or how men come to give assent contrary to probability. KNOWLEDGE being to be had only of visible and certain truth, ERROR is not a fault of our knowledge, but a mistake of our judgment giving assent to that which is not true. But if assent be grounded on likelihood, if the proper object and motive of our assent be probability, and that probability consists in what is laid down in the foregoing chapters, it will be demanded HOW MEN COME TO GIVE THEIR ASSENTS CONTRARY TO PROBABILITY.” source