Consider the sentence
6.1) mi [cu] vecnu ti ta zo'e seller-x1 sells goods-sold-x2 buyer-x3 price-x4 I sell this to that for some price. I sell this-thing/these-things to that-buyer/those-buyers. (The price is obvious or unimportant.)Example 6.1 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:
6.2) mi ti [cu] vecnu ta seller-x1 goods-sold-x2 sells buyer-x3 I this sell to that. (translates as stilted or poetic English) I this thing do sell to that buyer. 6.3) mi ti ta [cu] vecnu seller-x1 goods-sold-x2 buyer-x3 sells I this to that sell. (translates as stilted or poetic English) I this thing to that buyer do sell.Examples 6.1 through 6.3 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.
6.4) ta [cu] melbi object/idea-x1 is-beautiful (to someone by some standard) That/Those is/are beautiful. That is beautiful. Those are beautiful.when the x1 is omitted, becomes:
6.5) ________ [cu] melbi unspecified-x1 is-beautiful (to someone by some standard) Beautiful! It’s beautiful!
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.