Consider the sentence

Example 2.16 has one sumti (the x1) before the selbri. It is also possible to put more than one sumti before the selbri, without changing the order of sumti:

Example 2.16 through Example 2.18 mean the same thing. Usually, placing more than one sumti before the selbri is done for style or for emphasis on the sumti that are out-of-place from their normal position. (Native speakers of languages other than English may prefer such orders.)

If there are no sumti before the selbri, then it is understood that the x1 sumti value is equivalent to zo'e ; i.e. unimportant or obvious, and therefore not given. Any sumti after the selbri start counting from x2.

when the x1 is omitted, becomes:

Omitting the x1 adds emphasis to the selbri relation, which has become first in the sentence. This kind of sentence is termed an observative, because it is often used when someone first observes or takes note of the relationship, and wishes to quickly communicate it to someone else. Commonly understood English observatives include “Smoke!” upon seeing smoke or smelling the odor, or “Car!” to a person crossing the street who might be in danger. Any Lojban selbri can be used as an observative if no sumti appear before the selbri.

The word cu does not occur in an observative; cu is a separator, and there must be a sumti before the selbri that needs to be kept separate for cu to be used. With no sumti preceding the selbri, cu is not permitted. Short words like cu which serve grammatical functions are called cmavo in Lojban.