Lesson 9. Logical conjunctions#

Logical conjunctions in Lojban are based on 4 primitive ones: .a, .e, .o, .u. In this lesson, we'll cover them in detail.

Logical conjunctions for arguments#

Here are the conjunctions combining two words: this and that.

• ti .a ta = this and/or that

mi ba vitke le mamta .a le tamne I'll visit the mother or the cousin.

Note that .a can also be translated as at least one of the two values, and thus leaves open the possibility that I will get around to visiting both of them at some point.

• ti .e ta = this and that

mi ralte le pa gerku .e le re mlatu I've got a dog and two cats. I keep one dog and two cats.

• ti .o ta = either this and that, or none

mi ba vitke le mamta .o le tamne I will visit either both the mother and the cousin, or none of them.

Note that .o can also be translated as not one of the two values, and thus denotes that I will get around to visiting both of them at some point or none.

• ti .u ta = this, and perhaps that, this whether or not that

mi ba vitke le mamta .u le tamne I'll visit the mother whether or not I'll visit the cousin.

.u just emphasizes that the second value does not affect the truth of the sentence.

Placing nai after a conjunction negates what is to the right of it. Placing na before a conjunction negates what is to the left of it:

• ti .e nai ta = this and not that

mi nelci la .bob. e nai la .alis. I like Bob but not Alice. I like Bob and not Alice

We can also say ti .e nai ku'i ta (this but not that) adding a flavor of contrast for the second argument.

• ti na .e ta = not this but that

mi nelci la .alis. na .e la .bob. I don't like Alice but I do like Bob. I like Alice not and Bob

This may sound a bit weird for English speakers (I like Alice not…) so you might prefer to swap the arguments and use .e nai instead: mi nelci la .bob. e nai la .alis. or even mi nelci la .bob. i mi na ku nelci la .alis. will mean the same.

• ti na .e nai ta = neither this nor that (none)

mi nelci la .alis. na .e nai la .bob. I don't like neither Alice nor Bob

Negating with other primitive conjunctions might not look intuitively usable, you can just learn them from examples:

• ti .a nai ta = this if that, for this the exclusive condition to happen is that

mi ba vitke le mamta .a nai le tamne I will visit the mother but for that to happen I need to visit the cousin.

Thus, ti .a nai ta means that ta is necessary (but may not be the only condition) for ti to be applied.

• ti .o nai ta = either this or that

mi ba vitke le mamta .o nai le tamne I'll visit either the mother or the cousin.

.o nai can also be translated as exactly one of the two values.

If I want to say that I will visit either the mother or the cousin but not both, I need .o nai (either/or). It's unlike .a (and/or) where I can visit both of them.

• ti na .u ta = doesn't influence (not this, but perhaps that)

• ti na .u nai ta = doesn't influence (not this, but perhaps that)

• ti se .u ta = perhaps this, and that

• ti se .u nai ta = perhaps this but not that

These are used for connecting arguments. For connecting parts of compound relations we use similar conjunctions: ja, je, jo, ju. So instead of the dot (pause) we use j here.

Logical conjunctions for sentences#

This is a more concise way of saying:

mi ralte le pa gerku .i je mi ralte le re mlatu I have a dog, and I have two cats.

.i je joins two sentences with a logical and, showing that both sentences are part of one thought and are true.

Here are examples of other conjunctions for sentences:

la .rome'os. cu prami la .djuliet. i je la .djuliet. cu prami la .rome'os. Romeo loves Juliet, and Juliet loves Romeo.

This means both statements are true, i.e., Romeo and Juliet love each other.

The same applies to other conjunctions:

la .rome'os. cu prami la .djuliet. i ja la .djuliet. cu prami la .rome'os. Romeo loves Juliet, and/or Juliet loves Romeo.

This means one of them loves the other, and perhaps both of them do.

la .rome'os. cu prami la .djuliet. i jo nai la .djuliet. cu prami la .rome'os. Either Romeo loves Juliet or Juliet loves Romeo.

Here, either Romeo loves Juliet (but Juliet doesn't love him), or Juliet loves Romeo (but he doesn't love her).

la .rome'os. cu prami la .djuliet. i ja nai la .djuliet. cu prami la .rome'os. For Romeo to love Juliet, it's necessary that Juliet loves Romeo.

This means that if Juliet loves Romeo, he definitely loves her, but he may love her anyway (the only impossible outcome is that Juliet loves Romeo but he doesn't love her).

la .rome'os. cu prami la .djuliet. i jo la .djuliet. cu prami la .rome'os. Either Romeo loves Juliet and Juliet loves Romeo, or neither of the two events happens.

This means that if Juliet loves Romeo, he loves her, and if she doesn't love him, he doesn't love her.

la .rome'os. cu prami la .djuliet. i ju la .djuliet. cu prami la .rome'os. Romeo loves Juliet whether or not Juliet loves Romeo.

Notice how we Lojbanize the name "Romeo": the combination "eo" is impossible in Lojban, so we used "e'o" and added a consonant at the end of his name.

Note that da refers to the same entity when several sentences are connected.

Logical conjunctions inside compound relations#

le melbi xunre fonxa beautifully red phones

le melbi je xunre fonxa beautiful and red phones

Other conjunctions also make sense:

mi nelci ro tu voi xajmi ja melbi prenu I like all persons who are funny or handsome (or both).

mi nelci ro tu voi xajmi jo nai melbi prenu I like all persons who are either funny or beautiful.

This might be explained if, for example, I find the qualities of humor and good looks incompatible, i.e., a mixture of the two would be just too much.

mi nelci ro tu voi xajmi ju melbi nanmu I like all persons who are funny (whether or not beautiful).

And once again, we shouldn't forget the difference between connecting arguments and connecting parts of compound relation constructs:

mi ba vitke le pa pendo .e le pa speni I will visit a friend and a spouse.

mi ba vitke le pa pendo je speni I will visit a friend-and-spouse.

The last Lojban sentence means that the friend is also a spouse.

Logical conjunctions for relation tails#

pu ku mi uantida la .soker. gi'e klama le zdani gi'e citka le badna I played soccer, went home, ate the banana.

uantida

non-official relation: $x_1$ plays the game $x_2$, participates in the game $x_2$

gi'e connects several relations into one with some terms shared. Look at this: It expands into pu ku mi kelci la .soker. i je pu ku mi klama le zdani … which would be lengthier.

With gi'e, we keep the head of the relation constant and specify terms after each of the relation construct (kelci la .soker., klama le zdani …).

Thus, when using gi'e, we have several relations in the tail joined together but having a common head.

gi'e has the same final vowel as in je and thus means and.

Other conjunctions for joining relation tails:

• gi'a for and/or
• gi'o nai for either … or
• gi'u for whether or not etc.

These conjunctions have the same ending as those in the .a, .o, .u series.

Terms in sentences with several tails#

Note that tenses as terms and tenses attached to the main relation of the relation make a difference when applied to sentences that contain several attached relations:

• A term in the head of the sentence is applied to all its tails:

mi ba'o cu citka le badna gi'e pinxe I no longer eat the banana and no longer drink.

Here, ba'o is applied to citka le badna gi'e pinxe.

• A tense word that is a part of the relation is applied to that relation only:

mi ba'o citka le badna gi'e pinxe I no longer eat the banana, but I do drink.

Here, ba'o is applied to the implied mi citka le badna relation only but not to the implied mi pinxe relation.

Choice questions#

Another type of English "or" can be found in questions:

— xu do pinxe le tcati .o nai le ckafi? — pinxe — Will you drink tea or coffee? — Yes.

That's a peculiar, but perfectly reasonable answer: Yes, I will drink tea or coffee.

This happens because "or" has several meanings in English:

1. A or B can mean either A, or B but not both. We use .o nai here.
2. A or B can mean A or B or both. We use .a here.
3. A or B? can be a question meaning select from A and B, which of them do you choose? We use ji here.

Thus, in the last case, we use a separate question conjunction ji:

— do pinxe le tcati ji le ckafi? — Will you drink tea or coffee?

Possible answers:

le tcati .e le ckafi Tea and coffee.

le tcati Tea.

le ckafi Coffee.

It is also possible to use conjunctions when replying:

.e — Both (the first and the second item is chosen)

.e nai — The first one (tea) (the first but not the second one is chosen)

na .e — The second one (coffee) (not the first but the second one is chosen)

na .e nai — Neither (not the first and not the second one is chosen)

You can ask questions in the same way about the other kinds of conjunctions we have looked at. The interrogative conjunction for relation tails is gi'i, for compound relations — je'i, for sentences — .i je'i.

Indirect questions are achieved by using ji kau:

Consider the waiter asks a visitor

- le'e dembi ji le'e rismi - The beans or the rice?

Once the visitor answers, the waiter knows whether the visitor wants to eat lamb or beef:

ba le nu le vitke cu spusku kei le bevri cu djuno le du'u le vitke cu djica le nu ri citka le'e dembi ji kau le'e rismi After the visitor replies, the waiter knows whether the visitor wants to eat the beans or the rice.

Forethought conjunctions#

ge do gi mi both you and I

ge nai do gi mi Not you but I

ge do gi nai mi You but not I

go nai do gi mi Either you or I

The forethought conjunction ge means and, but it's placed before the first argument term, with gi separating the two arguments. This series is parallel to other conjunctions: ga, ge, go, gu, as well as ga nai, ge nai, go nai, etc. The separator gi is the same for all of them.

Using these conjunctions is a matter of convenience:

mi citka ge nai le badna gi le plise I eat not the banana but the apple.

Here, like in English, not is stated before the first argument.

ge and words in this series can also be used for connecting relations:

ge mi dansu gi mi zgipli le pipno I both dance and play the piano.

zgipli

$x_1$ plays musical instrument $x_2$

le pipno

piano

.i ga nai pu zi carvi gi ca cilmo If it has been raining recently, it's wet now.