Chapter 10. Modals & Causality#

What Are Modals?#

Every numbered place in a gismu's place structure was chosen during language design. But real speech sometimes needs to attach extra information beyond those fixed slots — things like with what tool, because of what, for what purpose, in what language, and so on.

Lojban handles this with modal tags (sumti tcita): particles that introduce an extra argument with a specific semantic role. They come in two forms:

1. fi'o + selbri — build a custom modal from any relation word
2. BAI cmavo — pre-built shorthand modals for common roles

Both work the same way: tag goes directly before the argument that fills that role.

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fi'o: Custom Modal Tags#

fi'o followed by a selbri creates a modal meaning "filling x₁ of [selbri]":

mi viska do fi'o kanla le zunle I see you [x₁-of-eye: the-left-thing] → I see you with my left eye.

Here fi'o kanla means "in the role of x₁ of kanla (eye)" — so le zunle fills that role. The x₁ of kanla is the eye, so this says the left thing is the eye used.

Since we often want a place other than x₁, combine fi'o with SE conversion:

mi viska do fi'o se pilno le zunle kanla I see you [x₁-of-se-pilno: the-left-eye] → I see you using my left eye.

se pilno = "is used by x₂ to …" so x₁ of se pilno is the tool. le zunle kanla fills that tool slot.

The terminator fe'u closes a fi'o modal (usually elidable):

mi klama le zarci fi'o se pilno le karce fe'u I go to the store [by-means-of: the car] → I go to the store by car.

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BAI: Pre-built Modal Shorthand#

Because certain modal roles are needed constantly, Lojban provides ready-made BAI cmavo (selma'o BAI). Each is derived from a specific gismu and abbreviates fi'o [that gismu].

Here are the most useful BAI modals:

Causality:

Circumstance:

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Causality in Depth#

English has one word "because" where Lojban has four distinct causal relations:

rinka

x₁ (event) physically causes x₂ (event)

mukti

x₁ (event) is the motive/intention causing x₂ (event)

krinu

x₁ (event/fact) is the justification for x₂

nibli

x₁ (proposition) logically entails x₂

le spati cu banro ri'a le nu do djacu dunda fi le spati The plant grows because you water it. (physical causation)

mi lebna le cukta mu'i le nu mi tadni I take the book because [my motive is] studying. (intentional motivation)

la .sokrates. morsi binxo ni'i le nu ro remna cu morsi Socrates died because [logically] all humans die. (logical entailment)

la .djan. cpacu le pamoi se jinga ki'u le nu le skina cu melbi John gets first prize because [justification:] the film is beautiful.

These distinctions eliminate a vast amount of ambiguity inherent in English "because", "since", and "therefore".

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Modal Sentence Connection#

A modal tag can also connect two full sentences — saying the second happened because of (or caused, or was justified by) the first. Use .i + modal + bo in afterthought:

le spati cu banro .iri'abo do djacu dunda fi le spati The plant grows; [because] you water it.

Or use seri'a (= with effect) to connect in the other direction:

do djacu dunda fi le spati .iseri'abo le spati cu banro You water the plant; [therefore] it grows.

The -bo prevents the modal from grabbing the next sumti as its argument; without bo, .iri'a do would mean "because of you" (taking do as its sumti).

Forethought modal connection (signal before first bridi):

ri'a gi do djacu dunda fi le spati gi le spati cu banro Because you water the plant, it grows. (ri'a ... gi ... gi)

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Common BAI Examples#

mi tavla bau la .lojban. I speak in Lojban. (bau = in language)

mi cadzu sepi'o le tuple I walk using my legs. (sepi'o = with tool = legs)

do klama zu'e le nu do citka You go for the purpose of eating. (zu'e = for purpose)

mi viska do gau le drata I see you [done-by: another person] → someone else causes me to see you / someone shows you to me.

mi tavla do ca'i le turni I speak to you by authority of the governor.

ko tavla mi bai [ku] Talk to me under compulsion! → Talk to me whether you want to or not!

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Tense and Modal Together#

Modal tags and tense tags occupy the same structural position before the selbri. They can co-occur in any order:

mi pu klama le zarci zu'e le nu mi citka I went to the store for the purpose of eating.

mi ba cadzu sepi'o le karce ri'a le nu le karce cu spofu I will walk by means of (no, wait) — because the car is broken.

(Rethought: in practice you'd pick one modal per tag slot, or separate into multiple bridi.)

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Modal Selbri (BAI + ku)#

A BAI particle followed by ku (with no following sumti) becomes a standalone modal without a specific argument, meaning "in-the-relevant-way":

mi tavla bau la .lojban. bai ku I speak in Lojban under compulsion (bai = under compulsion, but who's compelling is unspecified)

mi cadzu sepi'o ku I walk using [some unspecified tool]

This lets you signal the type of relationship without specifying the filler — useful when the filler is obvious from context.

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Key BAI Quick Reference#

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Modal Negation#

Modals can be negated with nai after the BAI particle to assert the absence of that relation:

mi klama le zarci mu'inai I go to the store without motivation. (or: the motivation does not apply to my going)

mi klama le zarci ki'unai le nu mi djica I go to the store, not for the reason of wanting to.

This is modal negation — it negates the role the sumti plays, not the whole bridi. Compare:

• mi na klama le zarci mu'i le nu mi djica = It's not the case that I go to the store due to wanting to. (bridi negation — whole claim is false)
• mi klama le zarci mu'inai le nu mi djica = I do go, but not because of wanting to. (modal negation — the causal link is denied)

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Sticky Modals: ki with BAI#

Just as ki makes tenses sticky (persistent across bridi), it can also make modal tags sticky. Append ki to any BAI to set it as the default modal for subsequent bridi:

bau la .lojban. ki mi tavla .i mi cusku .i mi pensi [In Lojban (set):] I talk. I say. I think. (all three understood as happening in Lojban)

mu'i le nu mi prami do ki mi klama le zarci .i mi dunda le cukta [Motivated by loving you (set):] I go to the store. I give the book. (both actions share the same motivation)

Reset a sticky modal with the bare BAI + ki with no argument (or start a new ki binding):

do'eki = "unspecified relation (set)" — vague reset bau ku ki = reset to no specified language

Sticky modals are especially useful in narrative when a single circumstance or cause applies to a whole sequence of events.

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BAI reference (official selma'o)#

Every BAI cmavo is tied to a gismu’s place (see the dictionary gloss: “gismu modal, _n_th place …”). The list below matches cmavo.tsv / gismu.tsv in this repo — not every spatial direction (ri'u, zu'a, …) is a BAI; those are FAhA, used as tense tags, not modal fi'o-style tags.

Causality, result, and purpose

Agency, instrument, beneficiary

Comparison and superlative

Language, culture, category, conditions

Other common ones

Not BAI: kau (indirect-question marker, UI), zu'u (discursive “on the one hand …”, UI), ri'u (FAhA direction).

For the complete alphabetical list, use jbovlaste or another official cmavo index; this site’s dictionary data may also expose BAI entries programmatically.

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Modal Comparatives: mau and me'a#

Two BAI cmavo are especially useful for comparisons: mau (from zmadu, more than) and me'a (from mleca, less than). Their place structures:

Because what you typically want to specify is the basis for comparison (x₂ — the thing being compared to), these BAI are usually used with se conversion:

• semau — "more than [comparison basis]" (x₂ of zmadu)
• seme'a — "less than [comparison basis]" (x₂ of mleca)

la frank. nelci la betis. semau la meiris. Frank likes Betty more than [he likes] Mary.

The semau la meiris. gives the basis: Frank's liking for Mary is what Betty's is being compared to.

la frank. nelci la meiris. seme'a la betis. Frank likes Mary less than [he likes] Betty.

Same information, different emphasis.

Modal Relative Phrases: pe/ne + modal#

When a comparison applies specifically to a sumti rather than to the whole bridi, attach the modal using a relative phrase — pe (restrictive) or ne (incidental):

la frank. nelci la betis. ne semau la meiris. Frank likes Betty, who he likes more than Mary.

Without ne, semau la meiris. would attach to the whole bridi (comparing the event of liking to Mary, which is nonsense). The ne binds the comparative to la betis. specifically.

la frank. nelci la meiris. ne seme'a la betis. Frank likes Mary, whom he likes less than Betty.

This pattern works with many other BAI. Some common ones used with relative phrases:

Pure comparison (without asserting the main bridi):

le ni la frank. cu nelci la betis. cu zmadu le ni la frank. cu nelci la meiris. The degree to which Frank likes Betty exceeds the degree to which he likes Mary.

This asserts only the comparison — it doesn't claim Frank actually likes either of them.

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Connecting Modals Logically#

When two bridi differ only in their modal tags, Lojban lets you reduce them to a single bridi with a connected modal. The connection works like any other logical connective:

mi klama le zarci ri'a le nu lo gerku cu batci mi I go to the store because a dog bit me.

mi klama le zarci ki'u le nu mi djica I go to the store because (justified by) I want to.

To say both simultaneously:

mi klama le zarci ri'aje ki'u le nu … I go to the store because of [physical cause AND justified reason] …

Or in afterthought:

mi klama le zarci ri'a le nu lo gerku cu batci mi .i ji'a ki'u le nu mi djica

When a single event is both the physical cause and the motivation:

mi klama le zarci ri'a ce'e ki'u le nu lo gerku cu batci mi I go to the store [physically-because AND justification-because] a dog bit me.

The ce'e creates a termset: both modal tags apply to the same sumti simultaneously.

Logical connective + modal together: You can assert both that two bridi are connected by logic (.ije = and) and by a modal relation — the modal is glued after the logical connective, before bo:

mi nelci do .ije mi nelci la .djim. I like you, and I like Jim.

mi nelci do .iki'ubo mi nelci la .djim. I like you; justified by [the fact that] I like Jim.

mi nelci do .ijeki'ubo mi nelci la .djim. I like you and, with that justified by [the fact that], I like Jim. — both the .ije and the ki'u link apply.

When the two bridi differ only in one sumti, you can compress:

mi nelci do .eki'ubo la .djim. I like you and/because Jim. (sumti-level .e + ki'u + bo)

Forethought connectives stay either logical or modal — not mixed in one gi chain. See Chapter 8 for connective details.

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seBAI: General Conversion Rule#

Any BAI cmavo can be prefixed with se (or te, ve, xe) to shift which place of the source gismu is being filled:

• mau fills x₁ of zmadu ("exceeded by …")
• semau fills x₂ of zmadu ("more than …" — the comparison basis)
• temau fills x₃ of zmadu ("in property of …")
• vemau fills x₄ of zmadu ("by amount …")

This works for any BAI, not just comparatives:

The conversion mirrors SE on selbri: seBAI fills "the thing that [source gismu]'s x₂ is" relative to the BAI's argument.

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Irregular BAI shapes#

Most BAI cmavo are regular CV’V pieces cut from a gismu’s first consonant + two vowels. The 65 BAI cmavo include 36 regular CV’V forms and a set of irregular ones. The irregularities fall into four categories:

1. CVV form (monosyllables — no apostrophe):

2. Uses the 2nd consonant of the gismu (collision avoidance):

3. Based on a lujvo, not a bare gismu:

4. Irregular 2nd vowel:

do’e stands alone: it is the generic/vague modal not derived from any specific gismu. Use it when no other BAI fits.

You do not need to memorize all irregularities — dictionary entries list each BAI’s source. This table explains why mau is not zmu and why dictionaries look inconsistent at first glance.

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jai — modal conversion (full treatment in Chapter 4)#

jai turns the modal’s sumti into x₁ of the bridi, and shoves the old x₁ into fai when it still needs a slot. Chapter 4 has the full pattern (jai gau, se jai, etc.). One classic bau example:

la .lojban. jai bau cusku fai mi Lojban is the language of my expressing [something]. (la .lojban. = modal “language” place as x₁; mi = old speaker in fai.)

jai also has a non-modal abstraction use (sumti raising); Chapter 12 ties that together.

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Tense Stacking: The Imaginary Journey#

When multiple tense elements appear before a selbri, they are not redundant — each one extends the reference point established by the previous one. Think of it as taking an imaginary journey:

1. Start at the "default" reference point (usually the speech moment, nau).
2. The first tense element moves you to a new reference point.
3. The second tense element moves you again from that new point.
4. The selbri's event happens at wherever you've arrived.

mi pu ba klama le zarci I [past] [then future] go to the store.

Step 1: move backward to some past moment (pu). Step 2: from that past moment, move forward (ba). The result: I will go to the store at some point after that past moment — possibly still in the past relative to now, or possibly in the future.

This explains why pu ba ≠ ba and ≠ pu: it means "at some point after X, where X was in the past."

mi ba pu klama le zarci I [future] [then past] go to the store.

Step 1: move forward to some future point (ba). Step 2: from that future point, move backward (pu). The result: before that future moment, I go to the store — this describes something that will have already happened by a certain future time.

The imaginary journey applies equally to direction tenses (vi/va/vu) and event contours (co'a, ca'o, etc.), allowing very precise temporal-spatial descriptions.

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Summary#

• fi'o + selbri creates a custom modal tag from any relation word
• BAI cmavo are predefined shorthand modals for common semantic roles
• Four causal BAI: ri'a (physical), mu'i (motivation), ki'u (justification), ni'i (logical)
• Modal sentence connection: .iri'abo (because-of), .iseri'abo (therefore)
• Forethought modal: ri'a gi … gi (because [A], [B])
• BAI + ku = modal without specified argument (role implicit from context)
• BAI + nai = modal negation (that role does not apply)
• BAI + ki = sticky modal (persists across subsequent bridi until reset)

Modal comparatives:

• semau = more than [basis] (x₂ of zmadu); seme'a = less than [basis] (x₂ of mleca)
• Attach to bridi-level: la frank. nelci la betis. semau la meiris. = Frank likes Betty more than Mary
• Attach to sumti via ne/pe: la betis. ne semau la meiris. = Betty (the one he likes more than Mary)
• Without ne, a comparative modal attaches to the whole bridi — often nonsensical
• Pure comparison (no main-bridi assertion): le ni … cu zmadu le ni …

Connected modals:

• Modals can be joined by jeks: ri'aje ki'u = both physically-because and justified-because
• ce'e in a termset: both modal tags apply to the same sumti simultaneously
• Mixed logical + modal: .ijeki'ubo, .eki'ubo (logical connective + ki'u + bo)

Other:

• Many BAI are regular CV'V; mau, kai, rai, tai, do'e are common exceptions — see Irregular BAI shapes above
• jai + modal: Chapter 4; abstraction jai without modal: Chapter 12