Why do languages modify their words for different moods?

Question

At the bottom on Wikipedia's Grammatical Moods page they list a bunch of different moods, but not all of them. I have yet to find a list of all moods across languages (if you know of one please comment).

The reason for this post is I am trying to wrap my head around moods because they are not intuitive the way they are described.

My main thought/wondering/question is why the different moods are typically made as variations of a word root. It doesn't seem to be this way in English (we have chains of words to express modality, like "I probably will have something like that in the future". But in some other language you might have the verb "to have" be "foo" and that whole sentence be "inamanafoobaratimani". Whereas when you are having a sentence about objects like "The cat climbed up the big tree to eat its catch", the objects are typically separate, though the adjective/noun pairs might be one word like "arborissimo" or something for "big tree". But you don't have "cattreecatch" as one word in some language, at least I don't think. (I am brand new to this).

But anyways, another thing that factors into this is that it makes a lot of sense to have the count or the tense be a modification of the word base. Like "cloths" pluralizing with the "-s", or "clicked" with the "-ed", it is short and to the point and shorter than "click-in-the-past" or something like that. Or "click-more-than-one" for plural. From what I've learned so far, Chinese does keep separate words for making things plural or tensed, which is cool, but many instead modify the word.

What I don't understand is how exactly, or why exactly, mood is made as a modification of the word. I was just looking at Sanskrit verbs and at the bottom they say:

Taking into account the fact that the participial forms each decline in seven cases in three numbers across three genders, and the fact that the verbs each conjugate in three persons in three numbers, the primary, causative, and desiderative stems for this root when counted together have over a thousand forms.

Why do they do this? It seems so much more complicated and more to learn than having discrete words like "probably, maybe, might, possible, hope, etc.", rather than varying the word prefixes/suffixes to include these features. My question is WHY. Why do they do it like this? In any language? How does it evolve? Is there something inherent in the way we think particularly about commands/probabilities/emotions/etc. (but not objects, actions, or other "things") that causes us to make them modifications on bases, instead of just separate words? I'm thinking maybe by saying it in one word somehow feels better, which is why it's (so much more?) common. I don't know. I want to know some reasons why languages make these word modifications, rather than separate words, because it seems so much less efficient from a computer-science standpoint, but there must be some benefit if it's such a widespread phenomenon.

Answer 1

First things first:

The concept of "grammatical mood", like the concept of "word", is one of those things that works great within a language (as a tool to make a particular theory/explanation more elegant) but kind of breaks down when applied cross-linguistically.

For example, some languages have tense, aspect, and mood being orthogonal axes, where any given verb can choose one of each. In Latin, you can mix and match however you like between [present|past|future] [imperfective|perfective|aoristic] [indicative|subjunctive] (*).

In other languages, tense, aspect, and mood are combined into a single marking, and you can only choose one. In Lingála, "present", "recent past", "gnomic", "habitual", and "subjunctive" (†) all take up the same slot: every verb gets one and only one of them. Sometimes this combination is called a "TAM", short for "tense-aspect-mood" (or "tense-aspect marking" if mood isn't included).

Sure, you could break down the Lingála TAMs into tenses, aspects, and moods: recent past is a tense, habitual is an aspect, subjunctive is a mood. But it just isn't particularly useful to do so, since they're all mutually exclusive. You can't create a subjunctive habitual, for example, even though semantically "if I did this over and over" isn't nonsensical or anything.

In still other languages it's a mix: Ancient Greek mixes mood with tense (indicative can co-exist with any tense, but imperative, subjunctive, and optative are mutually exclusive with tense marking), but can mix and match moods with aspects to your heart's content.

Now, to get to your actual question…

Whereas when you are having a sentence about objects like "The cat climbed up the big tree to eat its catch", the objects are typically separate…

Define "typically"!

Many languages incorporate the subject into the verb: Latin tē amō "I love you" versus tē amat "she loves you", for example, has descendants all across the Romance languages.

Many others incorporate the object into the verb as well: Swahili nakupenda "I love you", unapenda "you love me".

Some languages take this to extremes: Rwanda aranahakizibakun-someesheesherereza "she is also making them read the book, using the glasses, to you, for me, in the house" (‡).

Other languages have agglutinative morphology, where a huge number of morphemes can be combined into a single word, with morphology taking over the job of syntax in other languages: Inuktitut Parimunngauniralauqsimanngittunga "I never said I wanted to go to Paris!" (§).

But anyways, another thing that factors into this is that it makes a lot of sense to have the count or the tense be a modification of the word base.

Why those things in particular?

Why the count but not the gender (Latin amīcus "friend (m)", amīca "friend (f)"), the size (Swahili nyumba "house", chumba "room", jumba "mansion", ka-umba "apartment (dialectal)"), the general type of object (Swahili Mswahili "Swahili person", Kiswahili "Swahili language", Uswahili "Swahili-ness")?

Why the tense but not the aspect (Ancient Greek epaídeusa "I taught (in the past)", epaídeuon "I taught (in the past, repeatedly or for a long time, what's important happened during the duration)", epepaideúkē "I taught (in the past, it was completed, what's important are the aftereffects)"), or the evidentiality (Turkish geldi "he arrived", gelmiş "I heard that he arrived"), or the polarity (Japanese amegafutteiru "it's raining", amegafutteinai "it's not raining")?

The choice of what to incorporate into the morphology, and what to give to the syntax instead, is pretty much arbitrary. Mandarin has basically no verbal morphology at all, relying on syntax and additional words for all of these. Inuktitut uses morphology for all of them, requiring syntax and extra words for basically nothing!

Modern English is somewhere in the middle of the road, but closer to the Mandarin side: we use verbal morphology to indicate past vs non-past, and third person singular versus everything else, and that's it. But that's just English; other languages do it differently.

I want to know some reasons why languages make these word modifications, rather than separate words, because it seems so much less efficient from a computer-science standpoint…

Not at all!

From an information-theory standpoint, all that matters in the end are the bits. Some languages use fewer words, but more bits of information per word (since there are more possible words). Other languages use more words, but fewer bits of information per word.

In the end, as a recent study showed, it all evens out. Some languages have more bits per word, some languages have more bits per syllable, but in the end, the fundamental rate of information transfer is always right around 39.15 bits per second. It seems like this is a sort of fundamental limitation of human biology, and languages will evolve to reach it, by whatever means necessary—there's tremendous selection pressure being applied every second of every day, after all!

Over time, languages evolve in different directions. Romance dropped a whole lot of Classical Latin's morphology, using extra words instead. Then it incorporated some of those extra words into the verb, turning them into affixes. Modern Romance languages use a mixture of both. The exact details seem to come down to the vicissitudes of fate—which indicates that the different options are about equally useful for communication, and the choice of one or the other comes down to historical accident more than anything else.

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(*) Morphologically, not all of these forms are completely distinct: the future subjunctive looks like the present subjunctive, the present perfective looks like the past aoristic, etc. But you can still mix and match freely, and Vulgar Latin took steps to separate out the ones that got too ambiguous (such as the present perfective ~ past aoristic combination).

(†) And more! Different authors list different numbers, but in my own work I've separated out thirteen morphologically distinct TAMs.

(‡) Example taken from Kimenyi (2002).

(§) Example taken from Mallon (2000).

Apart from those, all examples are my own. If there are errors in them, blame me.

Answer 2

Every time a language "decides" that it should be simpler to have discrete words to express ideas, somebody (the speakers) comes along and messes up the system, by creating idiosyncratic meanings ("kick the bucket", "look up the answer", "give X a break"), and by smashing stuff together into one word (who says "will not" anymore?). Languages are very short-sighted: they can't see the future, and they can't compute the consequences of lexicalization. Those speakers proto-Bantu could not foresee that turning their multi-word constructions with "go" into paradigmatic inflectional differences would eventually result is a somewhat arbitrary set of verb forms.

It is not any more complicated and it isn't more to learn if you have to learn a string of morphemes and rules for combining them, as opposed to having to learn the same number of words and rules for combining them. The word/morpheme distinction is vastly overrated. What is more useful is semantic compositionality and formal transparency. However, transparency and compositionality are at cross-purposes with compactness (information-richness). So you have a choice between a single brief span of sound where you have to look up the meaning and you get a lot of information, or you have to parse a longer sequence of sounds and compute the interpretation. While you have more expressive freedom if each piece of information has a unique form, you rarely need that freedom. A politeness marker has greatest utility in getting people to do things, and perhaps least utility when talking about things expected but non-realized in the past. Rather than having 6 dozen words that you have to independently string together to convey all of the things that "mood" conveys, you can just conventionally convey some of them simultaneously, forgoing the demand (which people do not have, except as an academic desideratum) for infinite informational precision. Conventionalizing useful packages of information into brief tags isn't that big of a cognitive deal.

Verbs are special, in the enterprise of constructing a proposition. Verbs have requirements that other things be specified, e.g. they need subjects, they may demand objects, or a specification about the proposition in terms of time. By gluing the parts together within the verb, you are guaranteed that the elements required for interpreting the non-argument parts of a predicate are "local", that is you don't have to go hunting through the sentence to find out whether the speaker is saying that the proposition is true or is saying that it isn't true, or that he wishes that it were true.

The problem of "mood" is that it is not a particularly coherent category in the set of things which are "not about the arguments". The terms "tense" and "aspect" have been assigned particular definitions in terms of what they convey; for those languages with negative inflections, we have "polarity". IMO the Wiki listing of "moods" is a fraction of the bits of information that is actually conventionalized into inflectional differences in verbs (though their category list is more informative). You don't find people talking about "focus moods", yet focus is often one of those things that is conventionally signalled by inflectional form (and it isn't tense, aspect or polarity). There is no grammatical term in the set of "moods" that refers to "denial of presupposition/assertion", but that's one of those things that can be signaled by inflectional choice.