  Let us say that two or more substances are compossible if and only if there is no contradiction between the predicates derivable from their CICs. For example, consider the two individuals, Don and Ron. One of Don's properties is being the tallest man (at time t); one of Ron's properties is also being the tallest man (at time t). Naturally, Don and Ron cannot then inhabit the same world. On the other hand, each could have the property being over 2 meters tall and be members of the same world. Now in Leibniz's fully developed metaphysics this example might not be considered a good one, since it is most likely the case that Leibnizian individuals are not to be thought of as constituted by such relational properties. Rather than thinking of compossibility in terms of the properties of substances, it might be easier to think of it in terms of the perceptions of substances. Certainly, Don and Ron cannot be said to be members of the same world if Don perceives the moon landing of Apollo 11 on July 20, 1969 and Ron does not (or would not)—and not simply because he does not have a television set, but because on his July 20, 1969, there is no United States of America, let alone a space program. From this, it should also be clear that the compossibility of substances in a world is another manifestation of Leibniz's thesis of the universal harmony of perceptions of substances.