In Slavic languages, such as Russian, clauses in conditional sentences generally appear in their natural tense (future tense for future reference, etc.) However, for counterfactuals, a conditional/subjunctive marker such as the Russian бы "by" generally appears in both condition and consequent clauses, and this normally accompanies the past tense form of the verb. See Russian grammar, Bulgarian grammar, etc. for more detail. While the material conditional operator used in logic (i.e.formula_1) is sometimes read aloud in the form of a conditional sentence (i.e. "if "p", then "q""), the intuitive interpretation of conditional statements in natural language does not always correspond to the definition of this mathematical relation. Modelling the meaning of real conditional statements requires the definition of an indicative conditional, and contrary-to-fact statements require a counterfactual conditional operator, formalized in modal logic.