made more nearly universal. The past passive participle has a doubled -- , while the same word used as an adjective has a single -- : This rule is partly guided by pronunciation, but the geminated pronunciation is not universal. The rule is therefore considered one of the difficult points of Russian spelling, since the distinction between adjective (implying state) and participle (implying action) is not always clear. A proposal in the late 1990s to simplify this rule by basing the distinction on whether or not the verb is transitive has not been formally adopted. Prepositional phrases in which the literal meaning is preserved are written with the words separated; when used adverbially, especially if the meaning has shifted, they are usually written as a single word: (This is extracted from a whole set of extremely detailed rules about run-together, hyphenated, or separated components. Such rules are essentially arbitrary. There are enough sub-cases, exceptions, undecidable points, and inconsistencies that even well-educated native speakers sometimes have to check in a dictionary. Arguments about this issue have been continuous for 150 years.) Punctuation Basic symbols The full stop (period) (.), colon (:), semicolon (;), comma (,), question mark (?), exclamation mark (!), and ellipsis (…) are equivalent in shape to the basic symbols of punctuation (знаки препинания ) used for the common European languages, and follow the same general principles of usage. The colon is used exclusively as a means of introduction, and never, as in slightly archaic English, to mark a periodic pause intermediate in strength between the semicolon and the full stop (period) (cf. H.W. Fowler, The Kingˈs English, 1908). Comma usage The comma is used very liberally to mark the end of introductory phases, on either side of simple appositions, and to introduce all subordinate clauses. The English distinction between restrictive and non-restrictive clauses does not exist: Hyphenation The hyphen (-), and em dash (—) are used to mark increasing levels of separation. The hyphen is put between components of a word, and the em-dash to separate words in a sentence, in particular to mark longer appositions or qualifications that in English would typically be put in parentheses, and as a replacement for a copula: In short sentences describing a noun (but generally not a pronoun unless special poetic emphasis is desired) in present tense (as a substitution for a modal verb "быть/есть" (to be)): Direct speech Quotes are