5 Preface كَلّا لَو تَعلَمونَ عِلمَ اليَقينِYusuf AliNay, were ye to know with certainty of mind,1 (ye would beware!)Three kinds of yaqīn (certainty of knowledge) are described in n. to 69:51. The first is certainty of mind or inference mentioned here: we hear from someone, or we infer from something we know: this refers to our own state of mind. If we instruct our minds in this way, we should value the deeper things of life better, and not waste all our time in ephemeral things. But if we do not use our reasoning faculties now, we shall yet see with our own eyes, the Penalty for our sins. It will be certainty of sight. We shall see Hell. See next verse. But the absolute certainty of assured Truth is that described in 69:51. That is not liable to any human error or psychological defect.