Updated: Mar 21, 2021
There are many things in the cosmo, even though we don't always know how to call them. To avoid confusion, and manage to survive in an ever-expanding universe, there are some tricks that we should all know. One of them is definitely to learn how to use correctly 'questo' & 'quello'.
The best way to start this article is with a story that began a couple of thousand years ago. The protagonist of this story is called Octavius, AKA Augustus, a young guy from Rome, who happened to be the first Roman Emperor.
One day he was posing for a statue when a UFO suddenly flew through the sky. You know, at that time they didn't know much about area 51 and similar, but he pointed that thing out and asked to his collaborators what it was. To commemorate that moment the statue was completed (as in the picture on the side) with an inscription that today might be translated as : 'Cos'è quello?'
While this story might be not totally historically accurate, or accurate at all, we often need to point out something that we don't know how to call, that maybe we don't want to name, or something that we already mentioned, but what word to choose? In Italian, the use of demonstrative adjectives ('aggettivi dimostrativi' [Ita]), helps who's listening, and the speakers, to define the location of a noun in space and time. Even though this talking about space and time seems to get closer to physics rather than languages we can gradually get closer to that.
To start, with 'aggettivi dimostrativi' are intended : Questo - Questa (singular) Questi - Queste (plural)
Quel / Quello - Quella (singular) Quegli / Quelli/quei - Quelle (plural)
A near place in the space-time
When the object of the discussion is closer to the person who is speaking, the choice would be 'Quest-', just as in English it would be with 'this'. In Italian, the difference regards the gender of the noun: if you have to refer to 'una penna' (a pen [eng] ) that you are holding with your right hand you would use 'questa' (fem., sing.), while if you are talking about the smartphone you are holding with the other hand you would use 'questo' (masc., sing.).
Now, imagine you have eight lovely puppies in your arms!
You would look at them and say 'questi cuccioli' (masc.,pl.) , and if you have 5 ducks next to you, you would say 'queste papere' (fem., pl.).
For what concerns the idea of time, the Italian language works at the same way, if you are talking about a moment that is near to you (and that can vary from a day to years) the choice would always be 'quest-'. - It's the 1st of January, and with a really bad hangover you are discussing with your friends your 'buoni propositi' ( 'new year's resolutions' ) for the new year. How would you refer to the year you are living / going to live? I would definitely go for 'quest'anno' [questo] (masc., sing.), and at the same time if I'm talking about the last few years of my life, I would use 'questi ultimi anni' (masc., pl.).
Far away with far too many plurals - quelli, quegli o quei ?
The 'near situation' sounds fairly simple, but what about the objects/situations that are in a galaxy far far away? The use of 'quell- o/a' works as the exact opposite of 'quest-', you use it when you need to indicate something that is not close to you, just like 'quel gatto' (masc., sing.) crossing the road, o 'quella macchina' (fem., sing.) driving fast down the hill! You can think of 'quelle papere' (fem., pl.), we talked about earlier (far in time) or 'quei cuccioli adorabili'! (masc., pl.). But why do we have 'quel/quello' for singular, and 'quelli quegli, and quei' for the masculine plural?
The reason is related to Italian phonemic, in the case of singular masculine use the options are 'quel' or 'quello'. In this case, the demonstrative adjectives follow the same rules of the determinative articles : if a noun starts with [s + consonant], z, ps, y, gn, or ps, the choice would be 'quello' - e.g. if you are pointing out 'uno scatolone' ['a big box'] you would say 'quello scatolone' - while 'quel' will work for all the other nouns - e.g. 'quel gatto', 'quel cane'. If the noun is feminine the option will anyway be 'quelle'.
The plural masculine forms offer more options but they hold the same core rules. When the name that follows the adjective starts with a [vowel + a consonant], with [s + consonant], z, ps, y, gn, or ps , the right form would be 'quegli' - e.g. Quegli adulti ['those adults'], quegli insegnanti ['those teachers'],or quegli elefanti ['those elephants']; When the noun starts with any other consonant the choice would be 'quei' - e.g. Quei cani ['those dogs'], quei gatti ['those cats'], quei computer ['those computers'].
...and what about quello/quelli ?!
'Quello'/'quelli' are parts of the aggettivi dimostrativi, but they both have double function and they are often used as pronouns. If we think at that sentence allegedly attributed to Augusto at the beginning of this article, he asked 'What's that?' - 'Quello' was used to indicate something not specified: an unidentified flying object, far from the speaker.
Augusto used 'quello' to replace a name, so as a pronoun, and we constantly do that when we speak, but this topic will be discussed in another post! To sum up :
Quest- forms are used to indicate elements that are close to the speaker, in the space or time; Quell- [and variants] refer to elements that are far from the speaker. These forms can be used as pronouns to replace nouns that were already mentioned in a conversation or that can be understood due to the context.
P.S. There are other demonstrative adjectives > codesto, codesta, codesti, codeste;
but to be honest, as an Italian speaker, I've never used any of them in 30 years of my life.