continuity of the previous state (istishab) as to time and its related affairs

using analytical method of usul al-fiqh, the present essay deals with opinions of shiite usulis on this question whether continuity of the previous state can be used with regard to time, temporal affairs, and affairs conditioned upon time. as for the first, we investigate opinions of usulis in this connection first, answer the problem of lack of doubt as to subsistence and that of lack of unity between what is certain and what is doubtful secondly, and prove that the said continuity of the previous state is correct because of existence of customary unity between what is certain and what is doubtful. in the same way, continuity of the previous state as to temporal affairs can be exercised whether in the form of continuity of the previous state of the very existence or in the form of that of incomplete existence, and the doubt cast that this continuity of the previous state proves intellectual effects and hence is not acceptable is unjustifiable. as for duties or obligations conditioned upon time, if the time is not a condition of compulsion, continuity of the previous state can be exercised, but if it is a condition of the mandatory act it cannot be exercised as it proves intellectual effects of what is treated as being subsistent.