First Steps in Lojban
Lesson 15. Copulas: me and du

Let's take a break from tags for a bit and talk about copulas—the "be-verbs." Specifically, how to say things like “A is B” when B isn't just a simple predicate.

You mean like when we're setting two things equal to each other?

Something like that. Remember, we already have sentences like ti mlatu (this is a cat) or ti bloti (this is a boat), which don't need any extra words for "is."

True. But I still don't know how to say something like "This is Sora" or "That is the specific boat we were talking about."

Good point! Lojban handles this in a few ways. Let's start with me.
- me
- Before a sumti: selbri meaning “x1 is among / identical with [that sumti]” (see dictionary for full places).

When you say A me B, you're saying one of three things: that A is among the items in group B, that A is identical to B, or that A's group is a subset of B's group.
Basically, think about "the things A points at" and "the things B points at":
- If every thing A refers to is also something B refers to, you're using me (it's either a member of B or a sub-group of B).
- If A and B refer to exactly the same set of things, that's identity (co-reference).
In simple terms: everything that is A is also B.

Rough picture: what A refers to is covered by what B refers to.
For example:
lo vi nanmu cu me lo dinju cikre This man is one of the building-repair crew.

Be careful! me is not used to talk about literal parts of a whole (like a wheel being part of a car). For that, we use the word pagbu.
lo vi klupe cu pagbu le minji This screw is a part of the machine.

Got it. pagbu for the "part-of" relationship, and me for "membership" or overlap.

If you want to express strict identity (A and B are exactly the same thing), we use the word du.
- du
- x1 is identical to x2
ti du la .mikan. This is Mika.
tu du le bloti That is the boat.
du, like me, is a cmavo that can act as selbri.
True or false
Pick whether each statement is true or false according to the lesson.
me is basically glossed as “one/some among …”.
du expresses identity and can be used as a selbri even though it is a cmavo.
If A du B, then A me B always holds too.