I determine first the logical character of each proposition, finding the first to be an A, the second an E, the third an O and the fourth an I. Then I recall that in obversion the predicate must always be _negated_ and an A must be changed to an E or an E to an A; also an I must be changed to an O or an O to an I. Hence, the obverse of each proposition is: (1) “No earnest teacher is a not-diligent student.” (2) “All self-respecting men can afford to be not-careless (careful) in their personal appearance.” (3) “Some of the great teachers of the past did not-practice (failed to practice) what they preached.” (4) “Some weeds are not not-beautiful.” (4b) Infer by obversion from the following: (1) “All roses are beautiful.” (2) “None of the members of the stock exchange are dishonest.” (3) “Some pupils are not industrious.” (4) “Some teachers are tactful.” (5a) Convert the following: (1) “All that glitters is not gold.” (2) “All good men are wise.” (3) “Some books are to be chewed and digested.” (4) “No man is perfectly happy.” It is first necessary to determine the logical character of each proposition. Carelessness might lead one to call the first proposition an A because it is introduced by the quantity sign “_all_.” But on second thought we note that the meaning is to the effect that _some glittering things are not gold_; this is an O. It is clear that the second is an A, the third an I and the fourth an E. It is now expedient to recall the rules regarding conversion. These are, (1) do not distribute an undistributed term; (2) do not change the quality. We may now attempt to interchange the subject and predicate of each proposition, with the following results: (1) Conversion impossible. (2) “Some wise men are good men.” (3) “Some things to be chewed and digested are books.” (4) “No perfectly happy being is a man.” When attempting to convert proposition (1), I find that the subject which is undistributed becomes distributed, hence the rule pertaining to distribution is violated. This conclusion is verified by recalling the fact that an O proposition cannot be converted. The second proposition, being an A, is converted by limitation; while the third and fourth are converted simply, as is the natural procedure with all I’s and E’s. (5b) Convert these propositions: (1) “Blessed are the meek.” (All the meek are blessed.) (2) “None but material bodies gravitate.” (All gravitating bodies are material.) (3) “Gold is not a compound substance.” (4) “Usually cruel men are cowards.” NOTE.――_The first proposition is poetical while the second is an exclusive._ (6a) Contravert the following propositions: (1) “All virtue is praiseworthy.” (2) “Some teachers are not tactful.” (3) “A man who lies is not to be trusted.” Contraversion consists in obverting first, and then converting; consequently, the contraverse of the three propositions is as follows: