One ordinarily thinks of "reform" as a future-oriented process. But in time-keeping, reform can also affect the past, or at least how we shall record it in the future.

In some instances of calendar reform it was deemed necessary to extend the reforming calendar's beginning back before its day of institution. In such cases, the reformers decree that past days, months or years shall be referred to by designations those days, months or years did not have when they occurred.

The calendar of the French Revolution is a good example. It was adopted in October 1793, but it was then regarded as having begun over a year earlier, on September 22, 1792. Since the period following September 22, 1792 was to be known as Year I of the Revolution, "The Republican Calendar" was officially adopted in its second year, early in Year II of the Revolution.

Of course, then we can say that when Napoleon reinstated the Gregorian Calendar on January 1, 1806, he also reformed the past; for he did not then restart the calendar with the date, September 23, 1792. Restarting with the date January 1, 1806, implied that the (Gregorian) years between 1792 (or should that be '93?) and 1806 had occurred, when in fact, at least since late in 1793 no one officially counted or recorded those years in France with those designations.

The idea of "Retroactive Reform" can be understood in at least two ways. Either these reforms really do alter the names or designations of past times; or they just alter the way people will refer to the past times after the reform.

The first way of looking at it seems to allow for alterations of the past, something ordinarily thought impossible.

The second way of looking at it may thus seem more reasonable. But it leads to some odd confusions. For it suggests that the names or designations of past times are fixed by whatever people call those times when they occur. That is why retroactive reform can't really alter names or designations or past times, and so can only alter future references to them.

To see what's so confusing about this result, check out the next puzzle: "Clash of the Calendars."