_The Individual Proposition._ An individual proposition is one with an individual subject such as “Aristotle was wise.” In logic, the individual proposition is classed as a universal. This seems to be a bit irregular, as with the individual proposition there is no particular, while, the strictly _logical_ universal _always_ implies a particular. Because of this variation from the true logical form the relations, as indicated by the square of opposition, do _not_ apply to the individual proposition. For example: According to the square A and E are contrary, but, when individual, A and E contradict each other, as “Aristotle was wise” (A)――“Aristotle was not wise” (E). CHAPTER 10. IMMEDIATE INFERENCE (CONTINUED)――OBVERSION, CONVERSION, CONTRAVERSION AND INVERSION. (2) _IMMEDIATE INFERENCE BY OBVERSION._ _Obversion is the process of changing a proposition from the affirmative form to its equivalent negative or from the negative form to its equivalent affirmative._ Some authorities refer to this process as “Inference by Privitive Conception,” but Obversion seems to be a better term. Obversion is based upon the principle that _two negatives are equivalent to one affirmative_. With this double negative principle in mind let us experiment with the four logical propositions, A, E, I, O. _The A Proposition._ Example: “All thoughtful men are wise.” Insert the double negative and the proposition reads: “All thoughtful men are not not-wise.” Changed to the logical form this becomes: “No thoughtful men are not-wise.” Simplified and we have, finally: “No thoughtful men are unwise.” Thus by the process of obversion we have passed from the original proposition, “All thoughtful men are wise,” to “No thoughtful men are unwise.” In the first proposition the subject “_thoughtful men_” is denied of the predicate “_unwise_.” Assuming that “unwise” is the contradictory of “wise,” then: “What is affirmed of a predicate may be denied of its contradictory.” Recourse to circles will make this clearer. In the previous chapter it has been suggested that _not_ bisects the world. For example: What can _not_ be included in the _wise_ class may be placed under the not-wise or _unwise_ class. Likewise a circle bisects space――there is the space inside the circle and the space outside the circle. Let the space inside the circle represent all wise beings, then the space outside the circle would represent all not-wise or unwise beings; e. g., Illustration: FIG. 5. Now representing _thoughtful men_ by a smaller circle and placing it inside the larger we have, Illustration: FIG. 6.