The following cmavo are discussed in this section:

It is sometimes inconvenient, in a situation where an abstract description is logically required, to express the abstraction. In English we can say:

which in Lojban is:

which has an abstract description within an abstract description, quite a complex structure. In English (but not in all other languages), we may also say:

where it is understood that what I try is actually not the door itself, but the act of opening it. The same simplification can be done in Lojban, but it must be marked explicitly using a cmavo. The relevant cmavo is tu'a, which belongs to selma'o LAhE. The Lojban equivalent of Example 11.66 is:

The term “sumti-raising”, as in the title of this section, signifies that a sumti which logically belongs within an abstraction (or even within an abstraction which is itself inside an intermediate abstraction) is “raised” to the main bridi level. This transformation from Example 11.65 to Example 11.67 loses information: nothing except convention tells us what the abstraction was.

Using tu'a is a kind of laziness: it makes speaking easier at the possible expense of clarity for the listener. The speaker must be prepared for the listener to respond something like:

which indicates that tu'a le vorme cannot be understood. (The terminator for tu'a is lu'u, and is used in Example 11.68 to make clear just what is being questioned: the sumti-raising, rather than the word vorme as such.) An example of a confusing raised sumti might be:

This must mean that something which John does, or which happens to John, occurs frequently: but without more context there is no way to figure out what. Note that without the tu'a, Example 11.69 would mean that John considered as an event frequently occurs – in other words, that John has some sort of on-and-off existence! Normally we do not think of people as events in English, but the x1 place of cafne is an event, and if something that does not seem to be an event is put there, the Lojbanic listener will attempt to construe it as one. (Of course, this analysis assumes that djan. is the name of a person, and not the name of some event.)

Logically, a counterpart of some sort is needed to tu'a which transposes an abstract sumti into a concrete one. This is achieved at the selbri level by the cmavo jai (of selma'o JAI). This cmavo has more than one function, discussed in Section 9.12 and Section 10.22; for the purposes of this chapter, it operates as a conversion of selbri, similarly to the cmavo of selma'o SE. This conversion changes

into

In English, the subject of “cause” can either be the actual cause (an event), or else the agent of the cause (a person, typically); not so in Lojban, where the x1 of rinka is always an event. Example 11.70 and Example 11.71 look equally convenient (or inconvenient), but in making descriptions, Example 11.71 can be altered to:

because jai modifies the selbri and can be incorporated into the description – not so for tu'a.

The weakness of jai used in descriptions in this way is that it does not specify which argument of the implicit abstraction is being raised into the x1 place of the description selbri. One can be more specific by using the modal form of jai explained in Section 9.12: