I wonder if this might be a clearer way to think about it: Tio always answers kio, and tiu always answers kiu.

This holds true. We just must not forget to make a distinction between the demonstrative pronouns tio and tiu on the one side, and the demonstrative determiner (article) tiu on the other.

Kion vi aŭdis? -> Mi aŭdis tion. Here tio is a pronoun.
But: Kion vi aŭdis? -> Mi aŭdis tiun mensogon. Here tiu is a determiner.

The problem is the overlap of the -iu words: Kiu means both who (Kiu alvenis?) and which (Kiun filmon vi spektis?). Tiu means both that one (Tiu estas mia) and that (Tiu filmo estas mia).

Metsis, the fact that you have 8 points of correct on a brief four-sentence paragraph is not encouraging LOL. Why do I suck so bad at this language after spending so much time trying to learn it?

Thanks also for your previous comments. I'm looking over it all and taking it in.

Metsis:
1. To watch something (movie, play…) to the finish is traspekti ← tra + spekti. Note, that "watching" here is not a gerund (spekt_nt/) but a deverbal noun, which would be spektado in Esperanto.

Is this verb traspekti your own creation? It does not appear in either of the dictionaries I use.

Metsis:2. To make easier to denote accusative use a descriptive text before the proper name. This has an additional advantage to make clear what the proper name refers to.

Wouldn't you still need an accusative on the name of the film? Furthermore, in casual conversation in which everyone knows it's a film, you wouldn't really say "the film The Suicide Squad" would you? It would be like saying, "last night I watched the film Jurassic Park." Everyone knows it's a film already.

Metsis:4. This is a tricky one. While English dictionaries give "however" for tamen, its use requires that you have somehow defined the "assumption" as tamen stands for that. In other words tamen cannot be used to introduce an exception.

• Seninfana estis la edzeco de la rabeno, tamen ĉirkaŭ li ne mankis vivado kaj moviĝado : The marriage of the rabbi was childless, however/nevertheless there was life and movement around him.

Here you first assume that childlessness causes a dull life, then you reveal an opposite state of affairs.

In your sentence you introduce a contrast, you could say in English "In contrast I did watch…", so kontraste.

Interesting. First I've ever heard of kontraste.

Metsis:7. If an adverb gets associated with a verb, as they usually do in Esperanto, the usual place is right before the verb.

But not incorrect to place it where I did though, is it? Wouldn't that go back to the word order in Esperanto being very flexible?

For instance, if you were to write "Truly I say unto you. . ." couldn't you write it as "Vere mi diras al vi. . ."?

Metsis:8. While I understand the use of a noun in English, and a noun would also be fine in my native language, I hesitate to use it this way in Esperanto. PIV gives for legendo only the meaning of a story. Here we are attaching a feature to a person, so I think an adjective suits better. PIV has examples legenda figruo, heroo.

I was wondering about that. I wasn't sure if it would work or not.

Metsis:
The third way uses adverbs, which have a wider use in Esperanto than in English. One of such uses is to denote time:

• ĉi tiu matene/lunde/semajnfine/… which are usually shortened to ĉi-matene/lunde/semajnfine/…

I don't really understand what you're saying about these adverbs. Can you provide some example sentences?

Metsis:
you use tiu to refer to the latter person in a sentence with two persons.

• La pentristo pentris modelon. Li estis nuda. : the painter was nude
  
• La pentristo pentris modelon. Tiu estis nuda. : the model was nude

Hmm. Interesting. I'll have to try to remember that.

RiotNrrd:I guess I still don't have it figured out when to use tiu and when to use tio.

I tend to do the following.

If the item being referred to...

1) ... is known to be a person, whether identified or not, use tiu, always. Tiu homo estas bona OR tiu (homo - unspoken) estas bona.
2) ... is identified in that sentence, use tiu. Tiu kato estas bona.
3) ... is not identified in that sentence, use tio. Tio estas bona.
4) ... is not identified in that sentence, but has been identified in an earlier sentence, you may use either, because one could make the case that the item is either not being identified in that sentence (tio), or is considered identified by the earlier sentence but elided in this one (tiu). Tiu (kato - unspoken) estas bona, OR tio estas bona.

Thanks for the rules of thumb. I will have to commit these to memory.

RiotNrrd:Never put tio in front of an identifying noun, even an elided one, since that would put two -o words in a row, which is not allowed.

What do you mean exactly by an "identifying noun"?

nornen:
(*) Why no accusative? Because it is a predicate noun over the object, and those are never marked for accusative. Compare: Mi pentris ŝin nuda.

I don't think I understand. It seems that, based on your very example here, you need an accusative on The Suicide Squad. After all, if you subbed in "la filmo" for The Suicide Squad you'd certainly need an accusative on filmo.

nornen:About tiu and tio.

Maybe the easiest rule of thumb is this one (tiu): Tio stands for "that thing" or "that fact". In all other cases use "tiu":
Tio estas mia domo. = That thing is my house.
Mi volas tion. = I want that thing.
La vetero estas bela. Tio min ĝojigas. = The weather is fine. That fact makes me glad.

But if it stands for "that one (and not the other)", then it is tiu:
Mi volas tiun kaj ne la alian. = I want that one and not the other.
Tiu estas mia domo. = That one (and not the other) is my house. Maybe better: Tiu domo estas mia.
Ĉu vi vidas tiujn tri homojn? Tiu (pointing with the finger at one of them) batis min. = Do you see those three men? That one hit me (not the others).

Cool, thanks for the info. I'll have to go over this and think on it.

RiotNrrd:The "that (thing in general)" versus "that (specific one)" distinction is useful to keep in mind.

I've seen this distinction pointed out before but then in practice I've seen tio used where, based on this rule, it would seem that tiu should be used. I can't think of any examples off the top of my head, but they were instances where the thing being referred to could be thought of as one thing out of a known group and yet tio was still used.

RiotNrrd:So tio is the answer to "what?" and tiu is the answer to "which or who?" Tiu is used for people exclusively for the same reason we don't use ĝi for people: in Esperanto people aren't objects, and kio\tio are about objects.

Okay, tiu always for people. That sounds like a good, hard, un-subtle rule that I can keep in mind. Thanks.

RiotNrrd:I have always found this distinction difficult to communicate because English tends to translate both tio and tiu simply as "that", which my rule is trying to avoid doing.

If only Zamenhof had just taken his inspiration from English on this one!

1. I admit that the verb traspekti does not show up in Tekstaro and by Googling you get only a handful of hits (none mine). However the preposition tra can be used as a prefix with the sence "de komenca ĝis fina loko" (from PIV).

2. Next time you watch an Esperanto Youtube-video and hear a non-Esperanto name, pay attention how it is introduced. This use of a descriptive text namely is quite a common way to introduce foreign words, usually names, into an Esperanto text. It is especially useful when the name ends in something that poorly accepts an Esperanto ending. By introducing a film with mi spektis la filmon The Suicide Squad you can later refer to it just by la filmo.

Of course you can leave the description out in your own diary entry, and you can opt to mi spektis The Suicide Squad-on or even to mi spektis filmon The Suicide Squad. Personally I would go for the latter one, because the name is a multipart one.

4. See kontraste in PIV

7. I guess, it is not outright wrong to have vere where it is in vere Clint estas… , but to my Esperanto-ears Clint vere estas… sounds more natural.

***

PMEG § 6.1. Bazaj reguloj por E-vortoj says

PMEG:
lunde = en la lundoj, en lundoj, en ĉiu lundo, en iu lundo, en lunda maniero

so instead of en ĉi tiu mateno you can say ĉi-matene, which is a very common way to shorten an expression showing that something happened in a certain time.

nornen:
Nu, mi ne spektis The Suicide Squad tuta*.

(*) Why no accusative? Because it is a predicate noun over the object, and those are never marked for accusative. Compare: Mi pentris ŝin nuda.

While technically Nornen is correct, this whole "nuda kontraŭ nude" thing (this a FAQ on Esperanto forums) causes so much confusion, that I would go with a clearer expression. The original text is

PrimeMinisterK:
Well, I did not finish watching The Suicide Squad. I watched about half of it and paused it.

The first sentence tells that you did not see the film completely. The second sentence precises this "not completely" to "about half". This "not completely watched" can be expressed ,IMHO, more clearly with "not watched to the end/the whole movie".
 

• Mi ne traspektis (la filmon) The Suicide Squad.
  
• Mi ne finspektis (la filmon) The Suicide Squad.
  
• Mi ne spektis la tutan filmon The Suicide Squad.
  
• Mi ne spektis (la filmon) The Suicide Squad ĝis la fino.
  
• Mi ne spektis (la filmon) The Suicide Squad ĝisfine.

But perhaps I am translating too freely here.

What do you mean exactly by an "identifying noun"?

A noun that is identifying the thing being waved at. I.e., a noun.

Nouns don't like being modified by other nouns, and tio, also an -o word, is no exception to that rule. You cannot say "Tio [X]o". You have to say "Tiu [X]o".

A corollary to this that may not be immediately obvious is that the word "tioj" therefore is only very rarely (if ever) a correct construction. Tio refers to general things by default, for which the idea of plurality usually makes no sense, and there's never another plural noun to back it up. So if you ever feel the need to use "tioj", just don't, and your odds of being correct increase dramatically.