This way of dealing with a book is constructive and positive as opposed to the negative method of critical reading. For we read for suggestion only; we carry forward some line of thought of an author, which is better for intellectual development than trying to find if he was wrong and where he was wrong. Not only is this positive method more interesting; in some respects it is better even for criticism. For in carrying forward an author’s line of thought, noting its consequences and implications and considering different cases where it applies, we find whether or not it leads to absurd conclusions; whether or not all concrete instances conform with it. It should be kept in mind that this method is not to be followed until the main text-book has been studied. Consequently when it is followed your mind will have been fortified by previous reading and thinking; valuable thoughts of an author will tend to impress you and be remembered, while his trite or erroneous ideas will tend to be ignored. But after all, what is important is not your attitude or method at the time of reading a book, but the thinking done later. The critical attitude has its shortcomings, for when we are on the lookout for an author’s mistakes we often miss the full significance of his truths. On the other hand when “reading for suggestion” we may too often allow an error to pass unquestioned. But both these disadvantages may be overcome if we do enough thinking afterward. Only one thing I must insist on: make sure you understand every sentence of a book. Do not “guess” you understand it. Do not slide over it in the hope that the author will explain it later. Do not work yourself into the belief that after all it is not really important. Rather than this, better by far do not read the book at all. Not only will you get little or nothing from it but you will be forming the worst of intellectual habits—that of thinking you understand when you do not. If you have made every reasonable effort to understand an author and then have not succeeded, write in the margin “I do not understand this,” or draw a line alongside the sentence or passage. If you have to do this too often you should put the volume aside for a time. It is either too advanced for you or it is not worth reading. As to the thinking you do after reading. Often problems connected with the subject of a book you have read may arise spontaneously in mind, or an objection to a statement may suddenly occur to you when thinking on some other topic. Of course when this happens you should not stifle your thoughts. But besides this, definite periods should be put aside for thinking on what you have read and on the problems you have written. I cannot insist on this too strenuously or too often.