I have a number of evidential categories available for use, as well as some relating to certainty, which I view as a separate issue (source versus certainty). But I hadn't put any thought into making their use mandatory. There are certainly advantages to making it impossible to hide information by making the inclusion of some information carrying categories necessary. But it seems to me that not all possible information is going to be relevant to all possible statements or circumstances, and that forcing everyone to always include evidentials, even when they aren't relevant, will carry a high price. There are probably aspects of speech other than evidentials that it would be advantageous to include in some circumstances. If the grammar requires that they all be included in every statement, then every statement will be overcrowded with irrelevant add-ons. Also, there's the problem of enforcement. If, for example, you require that each statement end with an evidential, then what will stop irritated users from simply omitting it? If you create a system of grammar such that each of the add-ons must, unavoidably, be merged into the words, perhaps by some mechanism similar to verb conjugation, then how many people would volunteer to use such an inconveniently complex language? In order to be successful, a constructed language must be designed such that many people will want to use it. Only a few have reached that peak, such as Esperanto, and Klingon.

I looked at the Wikipedia page for Ithkuil. It doesn't seem to be geared towards preventing cognitive errors, so much as packing as much information as possible into as few phonemes as possible. For most of them I can't see the point. In English I can say "Trees are green." in a few simple words. From the sound of it, in Ithkuil I'd have to pack in so much information about the trees that it would take me an hour to figure out how to write the sentence. Is the set of trees spatially contiguous, in a specific but unnamed forest? Or is this the set of all trees on earth, being denoted as members of an abstractly defined set? And how do I feel about the matter?

Also, the creator packed the phoneme set so tightly that I can't see how he's going to avoid a high rate of transmission errors. There comes a point where you've got so many vowel sounds that individual sounds are so close together in phonetic space that you can't reliably distinguish between them.

So far I've been going in the opposite direction. Rather than including multiple layers of meaning in each word by complicating the sounds and grammar, I've been planning to restrict meaning to one meaning per word, with each additional bit of information requiring more text to transmit, and no restrictions on what the user can leave out because it's irrelevant. It looks to me like Ithkuil goes in the opposite direction. Which isn't to say that there isn't some interesting material there. The creator seems to have broken down his informational overlays into unusual categories, such as "configuration", "affiliation", "perspective", and so forth. It would be interesting to read about why he selected the categories that he did. So there might be some interesting stuff there to borrow. But it seems that he gave up too much in the way of usability. What good is a language that decreases the frequency of common cognitive errors, if the only people who can use it are already so smart that they rarely make such errors?

I don't think ithkuil has the goal. Forcing people to be extremly specific doesn't promote clear thinking. A language should allow people to be vague if they want to be vage.

I also think you would have problems when you take an abstract of a scientific paper and try to translate it into ithkuil.

I took a look at Cniglic. It seems similar to an idea that I noted as a candidate for an eventual add-on, to use diacritic marks as emotion indicators. The problem that this was intended to solve is that it seems overly limiting to be restricted to the one emotion indicator "!", and to have to put it at the end of the sentence. I much prefer the idea of having many such indicators, and being able to apply them freely throughout sentences. Implementing them as optional diacritic marks above vowels seemed like the best bet. But I haven't gone anywhere with the basic idea, except that at one point I began looking for a "definitive" list of human emotional states. I don't remember ever finding a list that I thought was reliable.

I think a core feature of a new conlang should be that it has a systematized way to express concepts. After making my first draft of a language I decided to dig deeper into modern applied ontology. I would recommend Barry Smith's and Katherine Munn's
Applied Ontology: An Introduction. The better you understand the ontological structure of the world the better you will be able to design a language that can precisely describe the ontological structure of the world.

The result is that you really don't seem to get a lot of bang for your buck by monkeying around with your language design to try to increase the rate of information transmission.

If you have a sentence like "Four plus five is nine" that's very hard to transmit in a language like Pirahã that doesn't have a word for four but has only "one, two and many". It might be able to say two-two for four and two-two-one for five but it's really hard to express the sentence.

I think English does have cases where it's a bit like Pirahã. We have four cardinal directions and if we want to go in a 45° angle we say north-east.

Base 10 is integrated into our language in a way that we can't simply switch to base 12 or base 16 when we want to do so on a whim.

Another quite horrible case is the English word of "feel". It mixes so many different cases together. You don't have a similar distinction as between "see" and "look" for feel. Feel get's used both to thing inside your own body and outside. Láadan has:

loláad = to perceive internally, to feel a mental state or emotion, perceive with the heart (metaphorically). Passive internal feeling. "I feel sad."
lowitheláad = to feel, as if directly, another's feelings (pain/joy/ anger/grief/surprise/ etc.); to be empathetic, without the separation implied in empathy
dama = to touch, to feel with the skin. Active touching, feeling. "I am feeling the texture of the yarn." (see láad oyanan, passive touch)
náril = to feel internally, to fix your internal attention actively upon something, to-continue-to-present-time. Active internal feeling. "I am feeling angry." (see loláad, passive internal feeling)
láad oyanan = to perceive with the skin, to feel something on your skin, touch. Passive feeling. "The silk feels good to me." (see dama, active touch)

When you say "Alice is afraid of Bob", the sentence doesn't transmit whether the author is speaking about a feeling or an emotion. Modern psychology has distinct notions of feeling and emotion but it's hard to express it, because the language hasn't really caught up with it. That's again a situation where it's important to familiarize yourself with the modern ontology instead of simply copying the ontology of the existing language. Having a richer language that can express more shades of meaning is a reason for people write literature in the language instead of writing in English. Literature that also can't be easily translated back into English.

I ran into some research in which the rate of information transmission of various natural languages was compared.

I'm interested into that research. Can you link it?

I ran into some research in which the rate of information transmission of various natural languages was compared. It turns out that in languages that are spoken faster, as measured in phonemes per second, the information carrying content, measured in bits per phoneme, is smaller.

This doesn't seem likely to generalize reliably to specialist constructed languages. I believe that it is true it when it comes down to average people talking about everyday things, but specialist subjects use specialized jargon and a shared bank of knowledge to communicate very complicated ideas very quickly. As a simple example, words like xor and nand, once they are fully understood and become automatic, do increase the rate of information transmission; likewise introducing the concepts behind 'bacteria', 'molecule', and 'atom' results in much quicker communication about a certain aspect of the world.

If you are constructing a language to hold rational debate, it does make sense to increase information transfer by expecting, and teaching, the language learners to match complex concepts with simple words. This should mean, in practice, more information per phoneme per second in the targeted areas.

While there will be a trade-off between time spent learning the framework and ability to communicate quickly, most rationalists are happy to spend time learning useful frameworks.

I think the Chinese are more likely to adopt a culturally neutral conlang than one based on European roots like Esperanto.

What makes you think this? I've never heard of East Asian countries objecting to English on the grounds that it has European roots.

I understand the temptation. From the beginning I wanted to scrap parts of the alphabet and start over. From the pedagogical perspective, accepting the fact that children have to learn 4 versions of the same alphabet (capital and non-capital, print and cursive), makes me feel like I'm condoning torture. The only common English uses for the capitals are to set off sentence beginnings and proper nouns, both of which could be handled differently. And now that we're beyond the days of manual typesetting, the only justification for print fonts is that they're easier to read than cursive fonts. I'd love to find or create a non-capital, cursive font that's just as easy to read as print fonts, and then scrap three of the four alphabets. but even separated and with serifs, cursive fonts just never seem to be as easy on the eyes as print fonts. So I decided to stay with contemporary English conventions to enhance ease of learning for English-speaking adults.

All good points, and among the strengths of conlangs in general. It still amazes me that past efforts at reforming English spelling, like President Roosevelt's, weren't accepted.

Ideally, a listener (reader) should be able to identify the part of speech of a word immediately

I'm not so sure.

Knowing a word's part of speech is of limited use if you don't know its actual meaning. Learning a word's meaning generally tells you its part of speech too. If by some chance you have an idea of a word's meaning but not its part of speech (because of ambiguities as with "ship", or because you worked out what kind of thing it has to mean etymologically), that's often enough to work out what's going on anyway. What's the real benefit here of making the part of speech more visible? It sounds nice, but when does it actually help much?

It doesn't seem unreasonable to ask that every important case in which a preposition must be used should correspond to a distinct word.

I'm not so sure.

Inside view: there are really quite a lot of preposition-functions, and prepositions want to be short words, so if we insist on a separate preposition for every preposition-function we'll need to allocate a lot of short words for them. Short words are a scarce resource. The language will have to be clumsier in other ways.

Outside view: every language I know enough about (admittedly a small subset of the world's languages) overloads its prepositions. That's got to be some evidence that doing so isn't a terrible idea.

For example the word "hammer" is a noun but also a verb meaning "to hit with a hammer". "Ship" is a noun but also a verb meaning "to send by ship" and so on.

I'd say this probably happens much more often than native English speakers even realize. You mostly notice it as a beginner, if your native language does not have strict rules for word order (because you differentiate different types of words by their suffixes or something like that) so you can move the words freely around in your first language. And then you read some English sentence where every single word has two or more possible meanings, and it's like a puzzle with an exponential difficulty. And you feel like: WTF, how can these people even get any meaning across in such ambiguous language?

Then you learn the rule that when you see "X Y Z", then "Z" is probably a noun, and "X" and "Y" are adjectives that modify it (unless "Y" is a verb, which means that the noun "X" is doing the "Y"-action to the noun "Z"), which reduces the search space. And after enough practice your brain starts doing it automatically, so the ambiguity becomes invisible.

It's not possible to represent every possible set of relationships this way (you can't even say "adopted child of the gay spouse of my stepfather's brother", let alone variations on teacher and classmate). So what you're actually doing is creating a system that can easily represent some sort of relations, at the cost of making it more difficult to represent others.

I think you are confusing "easy to create a system for" and "most useful". It is easy to create a system which specifies "father of father of mother of father of..." It is hard to create a system which specifies things you would actually need to specify often. Your system is efficient in the first sense but not in the second sense.

Should "father" be "caiqne" rather than "caiqma" as your comment currently says?

I could count on one maimed hand the number of times I've needed to say "teacher of my teacher". That a language wastes short possible-words on such things is not obviously a recommendation.

[EDITED to add a missing space.]

This compounding system is mostly good, but there's a problem in the phonology:

caiqce = grandparent

My linguistics-trained but English-speaking brain refuses to accept "qc" as a valid mid-word consonant cluster, and insists on a phonology rule to put a vowel in between. (I realize there are several ways of mapping q and c into IPA, but none of them worked for me in this case.)

I personally don't like the neutral/beloved/despised distinction

The feminist linguist who designed Láadan thought that "patriarchal" languages weren't sufficiently emotionally loaded. I'd like to see how she'd write a newspaper article using those pronouns.

Sounds like a good addition to my reading list, although I just looked at her books on Amazon and the prices on most of them are outrageous (I couldn't sell a book for $28, let alone $280). But with luck it might be possible to dig up a list of the basic primitives, with commentary, on the internet somewhere.

On this recomendation I read her latest book Imprisoned in English. I think it would make a lot of sense to write the core dictionary of a new language in what Anna Wierzbicka calls mini-english.

That definition for example has Ekman's anger described as:

it can be like this:
someone thinks like this about someone else:
“this someone is doing some things now
this is bad
I want something to happen, it can’t happen if this someone does things like this
this someone knows this
because of this, I want to do something (bad) to this someone”
when this someone thinks like this, this someone feels something bad because of this,
like people often do when they think like this

The german word Wut get's described as:

it can be like this:
someone thinks like this:
“something bad is happening here now
I don’t want this
I want to do something to something because of this now, I can’t not do something

Anna then shows how the words aren't completely interchangable even when the German Wut is the nearest word to the English anger. This mini-english has also the benefit of being automatically translateable into a variety of languages.

Perhaps a special sort of quote symbol used to highlight metaphors?