EDIT: (Sorry I wrote this idiotically the first time, I didn't sleep much last night and it's late here!)

Basically I was using words like dum, duma, dume, dumo. ambaŭ, ambaŭa, ambaŭo... and someone told me that adding the grammatical endings would change the meaning of the word, instead of just changing its grammatical form like what I had assumed. It was suggested that I stop using the endings.

I tried to look in the dictionary to see if they really do change meaning but what I found, if they were even listed, wasn't really clear. So what do you think? (Example usages come in my post below this.)

marbuljon:Can I have a clear list of what the words that don't normally have -a, -e etc. on, mean when they have them? Ex: dum, duma, dume, dumo. ambaŭ, ambaŭa, ambaŭo...

I tried to look in the dictionary but what I found, if they were even listed, wasn't really clear. (And since some people might get the wrong idea, no, it doesn't matter if no one else says them with endings, I want to know for reasons like using them to teach people other languages.)

Look up the root in PMEG (http://bertilow.com/pmeg/detala_enhavo.html) and check under vortfarado.

Sorry, I meant to come back and clarify my post but I couldn't get back to the computer as fast as I thought. I was meaning to add that this is how I thought of them:

ambaŭ - both.
I eat both. Mi manĝas ambaŭon.
I both eat and go. Mi ambaŭe manĝas kaj iras.
I have both dogs. Mi havas ambaŭajn hundojn.

(If you just replace these it becomes clear - "I eat pasta. I rapidly eat and go. I have red dogs." )

prias - is regarding, is about

la ĉirkaŭoj - the surroundings

kaje - along with that (best translation I can think of for "and-ly" right now)

...and so on.

It makes perfect sense to me, but someone else was saying that when you add these endings to words like "dum", it changes the meaning of the word (ex. dum would change between "during" and "meanwhile" by adding an -e, and while I don't really see a difference there, apparently other people do). I didn't think it did, and thought that you could just add endings according to its grammatical need in the sentence (since that's how other words work of course). Then I asked two people, one thought the same as me and the other didn't know enough Esperanto to be able to think about it.

So I meant to ask more for personal opinions.

(Also, btw Makis, you don't have to quote the post that comes directly before yours.... it's pretty clear who you're responding to haha)

(Also, btw Makis, you don't have to quote the post that comes directly before yours.... it's pretty clear who you're responding to haha)

Sorry, old habits!

Here's couple of things off the top of my head.

marbuljon:prias - is regarding, is about

= temi

la ĉirkaŭoj - the surroundings

-> ĉirkaŭaĵo

It makes perfect sense to me, but someone else was saying that when you add these endings to words like "dum", it changes the meaning of the word (ex. dum would change between "during" and "meanwhile" by adding an -e, and while I don't really see a difference there, apparently other people do).

Dum montras tempodaŭron, = “en la daŭro de”. Dum staras antaŭ tempa aŭ aga esprimo:
Tondroj bruadis dum la tuta nokto

Dume = 1. “Dum tiu tempo”: Mi iros ĝin akiri en la urbo! dume sidu iom ĉe mia malsana infano!M.198

Reading the PMEG is fun! (especially the vortfarado section for each word.) Too bad it's just so damn long...

But what is the real difference between ĉirkaŭo ("surrounding??" ) and ĉirkaŭaĵo ("surrounding-stuff" )? I'll also translate the above since we're on the English forum:

"Dum" shows a timespan = "in the continuation (duration) of".
"Dum" stands before a temporal expression:
Thunders kept on being noisy "dum (during)" the entire night.

Dume = "dum (during) that time":
I will go to acquire it in the town! "dume (durationally)," sit some quantity at my sick child!
(= sit for some amount of time at the house/place where my sick child is)

So to put it in English, if we are being logical, it still seems like it should mean and work exactly as how it appears. Meaning that without the grammatical ending, the word has to go in front of the phrase but it can stand for any grammatical form needed (it can be an adjective or adverb etc). With the grammatical ending attached, it can move around as normal for its type and it has the set, clear meaning of that specific ending. Just like any other word, it doesn't magically change meaning with a simple addition of an -a or -o (just like how "viro" actually means "a male" and not "a male human" specifically, but due to the dictionary people get the impression that its meaing changes, perhaps this confusion is all only due to bad dictionary definitions):

dum = during (in English, "during" is apparently a normal verbform that's just leftover from an old verb, thus it would really be "dumante, dumanta" in Esperanto if we translated literally, eh?)

dumo = a duration
duma = durational
dume = durationally (not a word that really exists; we use "while" instead, which is apparently short for something like "the while that" )
dumi = to "durate" (also not a word that exists in English, but apparently the sense is the same as "to endure, to last" )

And then according to the dictionary, the meanings for the English words:
prepositional meaning: "throughout the course or duration of". substantival and adjectival meaning: "the time during which something continues". adverbial meaning: "during the time that; during which" .

You might be overthinking this a bit.

Dume = meanwhile. It has an adverbial role and is distinct from dum, which is a preposition that has to go before what it attaches to.

If a preposition does not have a vowel ending, it can only be used as a preposition. Adding -o, -e etc. as necessary removes this limitation.

ambaŭ - both.
I eat both. Mi manĝas ambaŭon.
I both eat and go. Mi ambaŭe manĝas kaj iras.
I have both dogs. Mi havas ambaŭajn hundojn.

This is not quite right. More standard would be to say:

I eat both: Mi manĝas ambaŭ. Or: Mi manĝas kaj unu kaj la alian.

I both eat and go: Mi manĝas kaj iras. Or: Mi manĝas irante/mi iras manĝante.
I have both dogs: Mi havas ambaŭ hundojn.

The -aŭ words are a bit odd because they can be several different parts of speech.

A general tip is not to use -e or -o with -aŭ words that are already serving adverbial or nominal roles, respectively. It's redundant. This is why you rarely see something like preskaŭe or ambaŭo.

On the other hand, -e is very useful for prepositional -aŭ. Consider:

Mi esperis ke li helpos, sed li anstataŭe foriris. - I hoped that he would come, but he left instead.

Also. Trying to translate a sentence word-for-word out of English might not work very well for two reasons: firstly, English is bad at overtly indicating parts of speech, which might lead you to mark the Esperanto equivalent incorrectly; secondly, English is quite idiomatic and some natural prepositional phrases are really awkward or even incomprehensible in literal translation.

Ambaŭ functions as an adjective and as a nominal, which is why Mi ambaŭ manĝas kaj iras sounds funny - you're trying to use it as a kind of conjunction, which is normally expressed via kaj ... kaj (like in Slavic and Romance languages).

Ambaŭ is essentially equivalent to the Slavic dual oba/obe, except it doesn't decline - at all. That's probably not much help to you, though.