Sureba, suruto and sitemo, which are conditional verb forms in modern Japanese, are used to express causality in a broad sense, and it is widely known that they become deverbalized in some cases. Verbs such as miru, a visual verb, iu, a locutionary verb, and omou, a thinking verb, get deverbalized when they take a conditional form, and they usually turn into postpositions, connective particles, connectives, or sentence adverbs.
However, no connection has been identified so far between usages of such deverbalized verb forms and those of general conditional verb forms. This study examines how the grammatical meaning and syntactic function of general conditional verb forms affect usages of deverbalized verb forms.
Due to the grammatical meaning of conditional verb forms, if an event in the subordinate clause of a complex sentence is expressed in a conditional form, another event is also implicated. For example, the sentence “If it rains, let’s take a taxi” implies a case of not raining, in addition to a case of raining that is mentioned explicitly. Such implication can be identified in usages of postpositions and sentence adverbs that indicate a rationale behind the judgement on, or the evaluation of, a person or object. If a postposition or sentence adverb signals a rationale behind the judgement on, or the evaluation of, a person or object, another rationale is also implied in addition to the explicit one.
In complex sentences, conditional verb forms connect the events of the subordinate and main clauses. Such a function is found in usages where conditional verb forms turn into connective particles and connectives. If conditional verb forms become deverbalized, the connective function expands from the sentence level to the text level. In other words, conditional verb forms simply serve as a connective element within a complex sentence, whereas they connect sentences if they get deverbalized and turn into connectives.