The following cmavo are discussed in this section:

The cmavo of selma'o ZAhO express the Lojban version of what is traditionally called “aspect”. This is not a notion well expressed by English tenses, but many languages (including Chinese and Russian among Lojban's six source languages) consider it more important than the specification of mere position in time.

The “event contours” of selma'o ZAhO, with their bizarre keywords, represent the natural portions of an event considered as a process, an occurrence with an internal structure including a beginning, a middle, and an end. Since the keywords are scarcely self-explanatory, each ZAhO will be explained in detail here. Note that from the viewpoint of Lojban syntax, ZAhOs are interval modifiers like TAhEs or ROI compounds; if both are found in a single tense, the TAhE/ROI comes first and the ZAhO afterward. The imaginary journey described by other tense cmavo moves us to the portion of the event-as-process which the ZAhO specifies.

It is important to understand that ZAhO cmavo, unlike the other tense cmavo, specify characteristic portions of the event, and are seen from an essentially timeless perspective. The “beginning” of an event is the same whether the event is in the speaker's present, past, or future. It is especially important not to confuse the speaker-relative viewpoint of the PU tenses with the event-relative viewpoint of the ZAhO tenses.

The cmavo pu'o, ca'o, and ba'o (etymologically derived from the PU cmavo) refer to an event that has not yet begun, that is in progress, or that has ended, respectively:

As discussed in Section 10.6, the simple PU cmavo make no assumptions about whether the scope of a past, present, or future event extends into one of the other tenses as well. Example 10.51 through Example 10.53 illustrate that these ZAhO cmavo do make such assumptions possible: the event in Example 10.51 has not yet begun, definitively; likewise, the event in Example 10.53 is definitely over.

Note that in Example 10.51 and Example 10.53, pu'o and ba'o may appear to be reversed: pu'o, although etymologically connected with pu, is referring to a future event; whereas ba'o, connected with ba, is referring to a past event. This is the natural result of the event-centered view of ZAhO cmavo. The prospective, or pu'o, part of an event, is in the “pastward” portion of that event, when seen from the perspective of the event itself. It is only by inference that we suppose that Example 10.51 refers to the speaker's future: in fact, no PU tense is given, so the prospective part of the event need not be coincident with the speaker's present: pu'o is not necessarily, though in fact often is, the same as ca pu'o.

The cmavo in Example 10.51 through Example 10.53 refer to spans of time. There are also two points of time that can be usefully associated with an event: the beginning, marked by co'a, and the end, marked by co'u. Specifically, co'a marks the boundary between the pu'o and ca'o parts of an event, and co'u marks the boundary between the ca'o and ba'o parts:

Compare Example 10.54 with:

which illustrates the combination of a TAhE with a ZAhO.

A process can have two end points, one reflecting the “natural end” (when the process is complete) and the other reflecting the “actual stopping point” (whether complete or not). Example 10.55 may be contrasted with:

In Example 10.57, the meal has reached its natural end; in Example 10.55, the meal has merely ceased, without necessarily reaching its natural end.

A process such as eating a meal does not necessarily proceed uninterrupted. If it is interrupted, there are two more relevant point events: the point just before the interruption, marked by de'a, and the point just after the interruption, marked by di'a. Some examples:

In addition, it is possible for a process to continue beyond its natural end. The span of time between the natural and the actual end points is represented by za'o:

That is, the teacher went on explaining after the class already understood the problem.

An entire event can be treated as a single moment using the cmavo co'i:

Finally, since an activity is cyclical, an individual cycle can be referred to using a number followed by re'u, which is the other cmavo of selma'o ROI:

Note the difference between:

and