16.4. Restricted claims: da poi

The universal claims of Section 16.3 are not only false but absurd: there is really very little to be said that is both true and non-trivial about every object whatsoever. Furthermore, we have been glossing over the distinction between everything and everybody and the other pairs ending in -thing and -body. It is time to bring up the most useful feature of Lojban variables: the ability to restrict their ranges.

In Lojban, a variable da, de, or di may be followed by a poi relative clause in order to restrict the range of things that the variable describes. Relative clauses are described in detail in Chapter 8, but the kind we will need at present consist of poi followed by a bridi (often just a selbri) terminated with ku'o or vau (which can usually be elided). Consider the difference between

Example 16.20. 

da zo'u da viska la djim.
There-is-an-X : X sees that-named Jim.

Something sees Jim.


Example 16.21. 

da poi prenu zo'u da viska la djim.
There-is-an-X which is-a-person : X sees that-named Jim.

Someone sees Jim.

In Example 16.20, the variable da can refer to any object whatever; there are no restrictions on it. In Example 16.21, da is restricted by the poi prenu relative clause to persons only, and so da poi prenu translates as someone. (The difference between someone and somebody is a matter of English style, with no real counterpart in Lojban.) If Example 16.21 is true, then Example 16.20 must be true, but not necessarily vice versa.

Universal claims benefit even more from the existence of relative clauses. Consider

Example 16.22. 

ro da zo'u da vasxu
For-every X : X breathes

Everything breathes


Example 16.23. 

ro da poi gerku zo'u da vasxu
For-every X which is-a-dog : X breathes.

Every dog breathes.

Each dog breathes.

All dogs breathe.

Example 16.22 is a silly falsehood, but Example 16.23 is an important truth (at least if applied in a timeless or potential sense: see Section 10.19). Note the various colloquial translations every dog, each dog, and all dogs. They all come to the same thing in Lojban, since what is true of every dog is true of all dogs. All dogs is treated as an English plural and the others as singular, but Lojban makes no distinction.

If we make an existential claim about dogs rather than a universal one, we get:

Example 16.24. 

da poi gerku zo'u da vasxu
There-is-an-X which is-a-dog : X breathes.

Some dog breathes.