You may at some stage have asked yourself the question, what the Lojban for is is. The short answer is, most of the time there isn't one. Lojban represents the world in terms of relations (bridi), and is is a fairly empty kind of relation. Moreover, if the thing to the right of is (the 'predicate', in grammar terminology) means a class of things, instead of a single entity, then it corresponds to a selbri, and we don't need to put a word for is in. So "Robin is English" comes out in Lojban as la robin. glico: glico is already a selbri that takes la robin. as a sumti — so we don't need a separate selbri for is.

Very, very, very occasionally, you'll need a Lojban word for is anyway. Lojban offers three words which sort of do the job of is; each has its own provisos.

The first word is me. me takes a sumti following it, and converts it into a selbri. So me la nik. is a selbri, which takes as a sumti anything that 'is a Nick'. Similarly, since le mi ci mensi is 'my three sisters', la renas. me le mi ci mensi means "Rena is one of my three sisters" (as she is described by the selbri version of 'my three sisters'.) So me is best thought of as meaning 'is one of'.

Historical note: me, way back in the dawn of (Lojbanic) time, used to mean 'pertaining to' instead of 'is'. You'll see confusion between the two persisting among old timers. Be gentle with them, we pray you...

The second word is du. du is a selbri on its own, and it means that all its sumti are the same thing and have the same identity. So mi du la nik. (or mi du la robin.) is a way of saying "I am Robin (or Nick.)" The claim made is one of identity; so you can flip the sumti around without making any difference: la robin. du mi. It does not make a sumti behave like a selbri, so du cannot mean 'is one of', like me does: la renas. du le mi ci mensi makes the nonsensical claim that Rena is my three sisters. (Or should that be are?)

Tip: Can you say mi du lo prenu, doing the Lojban equivalent of making an indefinite noun 'equal' a definite noun? After all, lo prenu applies to many more people in the world than just me, so du here does kind of act like 'is one of'.

The answer is, yes you can, because in this context they both do refer to the same person. (In strict logical terms: "there is at least one person such that that person is me.") This is frowned upon in Lojban in general, though, because it's misleading: du tends to be reserved for mathematical equality, and for claiming that two different names (or definite nouns) refer to the same thing. If you really wanted to say mi du lo prenu, after all, why wouldn't you just say mi prenu?

These two means are grammatical Lojban, but they are viewed with some distaste, and are usually giveaways that some poor translating from English (or another natural language) has been going on. The third mechanism is better regarded, because it tucks the equality away in an inconspicuous corner. po'u has the same grammar as the sumti modifiers like pe and po we saw in Lesson 3. But instead of claiming that one sumti is associated with the other, or owned by the other, po'u claims that the two sumti are the same thing. So:

la ranjit. po'u le pendo be la djiotis. vi zvati
Ranjeet, who is Jyoti's friend, is here.

Like those other members of selma'o GOI (pe, po and po'e), po'u has a non-restrictive version: no'u. So if I was saying that Ranjeet was Jyoti's friend, not to distinguish him from the other Ranjeets you might know, but just for your information, I should use no'u instead of po'u. You can think of no'u as tantamount to noi du, and po'u as tantamount to poi du.

Note: no'u and po'u are typically used in Lojban to introduce alternate names for something; so they correspond to English namely, i.e. For instance, la suzyn. penmi la xumske fanza ku no'u la jan. "Susan met 'Chemistry Annoyance', namely Zhang."



x1 is exactly/approximately half/semi-/demi-/hemi- of x2 by standard x3

Exercise 5

Where appropriate (and only where appropriate), translate is in each of the following sentences with each one of me, du, po'u, and no'u. To get po'u and no'u to work, you may have to rearrange the sentences. For instance:

x, which is [equal to] y, is a number.

  • da noi me de cu namcu

  • da noi du de namcu

  • da no'u de namcu

  1. Jyoti is a woman.

  2. Jyoti and Susan are the two women who went in Jyoti's car.

  3. Jyoti and Susan are among the women whom Zhang considers his friends. (Use jinvi.)

  4. Ranjeet, who is a friend of Jyoti, is half-German.

  5. This blue car which is the one to the right of mine is a Ford car. (Use le pritu for the one to the right.)