You have by now most likely figured out the reason, however for the next to look at the discussion section, I think this is the reason.
ti and te is both direct object pronouns used for the singular familiar you, however the difference is that ti is the unstressed (clitic) direct object pronoun whereas te is the stressed (tonic) direct object pronoun.
lo and lui is both direct object pronouns for the singular 3rd person him. Again the difference is that lo is the unstressed (clitic) direct object pronoun whereas lui is the stressed (tonic) direct object pronoun.
Unstressed (clitic) pronouns is placed before the conjugated verb, whereas stressed (tonic) pronouns are placed after the conjugated verb.
For this sentence, it is important that the speaker (io) sees you and not him (that specific guy over there) and therefore both the you and the him is stressed which is why the construction of verb and the first direct pronoun is structured like that.
Had it ie. been a random guy the lui would have been a lo.
Don't worry, you're not alone. I've taught English for over ten years and have never ever seen the word "clitic" in an English course book, nor is it mentioned in my Italian grammar book (published in Italy). I'd forget about clitics, and simply think of atonal object pronouns (mi, ti etc), tonic pronouns (me, te etc) and ne and ci.
I enjoy the clarity, but it does end up a little confusing. I think it has to to do with Duolingo's problem of having no context.
If I understand correctly, both answers are awkward because they contain clitics/unstressed pronouns that wouldn't be used in clarification.
That said, there may very well be situations where these sentences may be valid, but I don't know enough Italian to verify that.
My take is this, it is not a simple Ti vedo since it's implied that someone is saying, "Do you see him, too?" Since it's not a simple Ti vedo, the way you do that in Italian is this, "Vedo te, ma non lui" since you don't say "Vedo ti, ma non lo." If you pay attention to the positions, you start to see that it has to do with what a speaker is stressing and these terms of "clitic"and "tonic".
For the record, Sanne, I really appreciate the fact that you took the time to type this beautifully crafted, very thorough answer. I found your explanation clear and easy to read and understand. So many other people opt to just reply with a link to another website, but I find it much easier to read explanations given in the context of the question(s). Thank you so much!
They are just two different constructs. The closest to an english "mind" is:
Subject (optional) + verb + pronoun.
With this one, you have to use the stressed object pronoun, that is "te" in this case.
Io + vedo + te
I + see + you
If you want to stick to the other construct (subject + unstressed clitic + verb, "Io ti vedo"), you have at least to repeat the verb: "Ti vedo ma non lo vedo".
However, the result is a clumsy sentence, unless you have a good reason to do that, and you underline the two pronouns with the tone of your voice ("TI vedo ma non LO vedo")
An easier alternative could be "Ti vedo ma non vedo lui" (mixing the two constructs)
In short, yes. Lui and lei are used with both those cases, but in accusative case, they are stressed/tonic pronouns. Lo and la are the other accusative pronouns for the two, which would be the clitic/unstressed/atonic pronouns. You would not use them in every case, so to speak.
Have a look at the tips and notes for a bit more detail.
Scroll down at this page with your internet browser. https://www.duolingo.com/skill/it/Clitic-Pronouns-1
Struggling with this section - any one help? So ti is the unstressed (clitic) And te is the stressed (tonic) - got that BUT I just cannot see HOW to use them - which one to chose????? Likewise with me and mi etc Somehow I finally managed to complete the first lesson - but only by repetition
Am I being thick, or something?
I struggled quite a lot with this section myself, so I will try to see if I can help out. it all comes down to sentence analysis.
There is is verb and you already know a lot of different italian verbs. The verb is the action - it is the thing that does. As you know, the verb conjugates to fit the subject of the sentence.
The subject of the sentence is a kind of pronouns. You already know the subject pronouns which relates to the verb - the person/thing/name that does the action
I | io
you (familiar) | tu
you (formal) | Lei
he, she, it | lui/egli, lei/ella, lui/lei
we | noi
you (all) (familiar) | voi
you (all) (formal) | Loro
they (mas) | loro/essi
they (fem) | loro/esse
Something about pronouns:
Besides the subject pronoun there is other types of pronouns that you will get to know in this skill - direct object pronoun, indirect project pronoun and reflexive pronoun.
These pronouns is used in the sentence to replace the subject, so it isn't used all the time.
direct object and indirect object can be divided into unstressed (clitic/atonic) and stressed (tonic). I am not sure if reflexive also does, so I will not state that.
If a pronoun is unstressed it is placed before a conjugated verb, attached to the infinitive verb and for direct object pronouns placed after the italian negative non.
If a pronoun is stressed it is placed after a conjugated verb.
direct subject pronoun
The direct object pronoun is the recipient of the verb. It answers the question who and what.
In the sentence the cow drinks it the action is: drinks, the subject is: the cow, and what is the cow drinking: it = direct object.
English | unstressed | stressed
me | mi | me
you (familiar) | ti | te
him | lo | lui
her | la | lei
it | lo/la | lui/lei
you (formal mas+fem) | la | lei
us | ci | noi
you (familiar) | vi | voi
you (formal, mas) | Li | Voi
you (formal, fem) | Le | Voi
them (mas, mas+fem) | li | loro
them (fem) | le | loro
And for the sentence
the cow drinks it = (directly translates) la mucca beve lo = (moving the direct object in front the conjugated verb as written before using the unstressed version of the pronoun) La mucca lo beve
indirect subject pronoun
The indirect subject pronoun is the part of the sentence the subject actions the direct object and it answers the question to/for who/whom.
In the sentence we bring him a bottle of wine (a DL sentence), bring = verb, we = subject, what do we bring = the wine = the direct object, and to who do we bring the bottle of wine = to him = indirect object.
English | unstressed | stressed
to/for me | mi | a me
to/for you (familiar) | ti | a te
to/for him | gli | a lui
to/for her | le | a lei
to/for it | gli/le | a lui/lei
to/for you (formal mas+fem) | Le | a Lei
to/for us | ci | a noi
to/for you (familiar) | vi | a voi
to/for you (formal, mas+fem) | Li | a Voi
to/for them (mas+fem) | loro | a loro
And for the sentence
we bring him a bottle of wine = (directly translates) noi portiamo gli una bottiglia di vino = (moving the indirect object in front of the conjugated verb as written before using the unstressed version of the pronoun and leaving out the subject) gli portiamo una bottiglia di vino.
I tried to write it to the best of my abilities. I hope it can help you out a bit.
Hi, and thank you so much for your detailed reply. My head is spinning because I suspect I have had too much learning - so I have pasted it into my online notebook (I use OneNote) and and going to take some time studying it before I go back to Duolingo.
I know it will be a great help. Thanks again. LC
No LadyCarrington53, you are not being thick as I have found this section to be the most difficult and confusing that I have encountered so far.
'Gli' doesn't work here because it's a personal pronoun for the indirect object. The ones you may be asking about are 'lo' and 'ti.' However, 'lo' and 'ti' are not equivalent to 'lui' and 'te'; 'lo' and 'te' come before the verb. Therefore, you can say 'Lo vedo' or 'Vedo lui.' Broadly speaking, those two sentences share the same meaning, but they are used with different intentions: 'Ti vedo' states a fact in a neutral way; 'Vedo te' on the other hand, expresses the point emphatically, and is commonly used to mark a distinction with something else. That's why this exercise is written in that way: because in this case "I see you" is not used to state a fact in a neutral way, but to put an emphasis in the object; i. e. 'I see YOU, but not him.'
It sounds like the voice is saying, "Vedo te mano lui," which, of course, makes no sense, but it sounds this way only because the inflection that would be used to say "but not him" is missing. This happens sometimes with the female voice too, but it is mostly the male voice that elides words with a complete omission of emotion. I wish Duo would improve this, but I suppose it would require re-recording much that he says. Was no one listening when they did this the first time?