robinast:"tio" versus "tiu" means general versus specific, not literally thing versus person...

Personally I have never seen tio / tiu as general vs specific, and I still cannot grok that kind of differentiation. I think of the pair tio-tiu as concept versus numerable individual(s), and kio-kiu as clarification versus identification (with kia giving qualification). When you use "tiu(j)", your finger points to something external; you are pinpointing an item or a person for all to see. When you use "tio", you refer to something in the context, a concept, an idea or an object that either has been mentioned or is in your head.

Tiu estas, kiun mi volas.
That one is the one I want. (that book, that house, that shirt, that cat, etc).

Tio estas kion mi volas.
That's what I want. (world peace, esperanto being taught in school, a career in designing revolving doors, etc).

I would agree with mnlg.

My own personal usage of tio/tiu is that tio is used like a noun and that tiu is often used in an adjective sense, as it describes* something - I would try to explain my point of view further but it probably won't make sense, and being a learner myself I don't want to confuse you .

*when I say describe, I mean it is more or less attached to another meaning, whereas tio contains all the meaning as a noun would. Sorry, I'm not very good at describing these things :S

Good luck anyway!

Part of the confusion in tables of correlatives arising from labelling -o correlatives as 'object', is that the words do not refer to concrete 'objects' like houses or stones.

Page 22 of Teach yourself Esperanto says that kio and tio 'are used as pronouns for things that are unknown till named'.

I would say that tio refers to anything that is not clearly defined as a substantive ending in -o. It could be either something not yet named, or an incident occurring over an interval of time (like enjoying an ice cream).

The PMEG is in harmony with this interpretation (see also the cross-reference on that page).

Erinja's interpretation therefore seems to me to be quite sound, if the word 'general' is interpreted to include the meaning 'non-defined' as well as 'non-specific'.

This is consistent with the fact that tiu and kiu in isolation are taken as referring to persons, if the context does not indicate that any other well-defined thing is being referred to. That is a special case of a well-defined thing.