In the following passage, some of the words have been left out. Read the passage carefully and select the correct answer for the given blank out of the four alternatives.

People may see, and hear, and feel all their lives without ____________ learning the nature of things they see. But reason is the mind's eye, and enables us to see why things are, and when and how events may be made to happen ___________ not to happen. The logician endeavours to ____________ exactly what this reason is which makes the power of men. We all, as I havesaid, must reason well or ill, but logic is the science of reasoning and enables us to distinguish______________ the good reasoning which leads to truth, and the bad reasoning which everyday betrays people into error _________ misfortune.