12. If there be one negative in a clause, a second is not admissible.
13. In phrases answering the question "where?" (meaning direction), the words take the termination of the objective case; e. g. kie'n vi ir'as? "where are you going?"; dom'o'n, "home"; London'o'n, "to London", etc.
14. Every preposition in the international language has a definite fixed meaning. If it be necessary to employ some preposition, and it is not quite evident from the sense which it should be, the word je is used, which has no definite meaning; for example, ĝoj'i je tio, "to rejoice over it"; rid'i je tio, "to laugh at it"; enu'o je la patruj'o, a longing for one's fatherland". In every language different prepositions, sanctioned by usage, are employed in these dubious cases, in the international language, one word, je, suffices for all. Instead of je, the objective without a preposition may be used, when no confusion is to be feared.
15. The so-called "foreign" words, i. e. words which the greater number of languages have derived from the same source, undergo no change in the international language, beyond conforming to its system of orthography. — Such is the rule with regard to primary words, derivatives are better formed (from the primary word) according to the rules of the international grammar, e. g. teatr'o, "theatre", but teatr'a, "theatrical", (not teatrical'a), etc.
16. The a of the article, and final o of substantives, may be sometimes dropped euphoniae gratia, e. g. de l' mond'o for de la mond'o; Ŝiller' for Ŝiller'o; in such cases an apostrophe should be substituted for the discarded vowel.