This is the second part of my answer to Meri's letter. Part one is here. Here's Meri's letter again:
I have some questions regarding the verb ostaa and the behavior of some nouns and the endings they take. Ostaako Peter bussilipun? Minä ostan maitoa/ jäätelöä. Assuming that the sentences are correct, which I think they are, why is it that with the same verb variations to the noun are possible? What is the difference? When do we know which variation to use? Here are my suggestions/ problems. I know that the partitive case is used for nouns that cannot be counted Maito is one such noun. You cannot count the milk, but the containers in which it is stored. However, as I see it, jäätelö can be counted, or am I wrong? One more thing. How do say that I want for example to buy tickets to a concert, for one, then the tickets to a particular concert? Would these be correct? Minä haluan ostaa lipput. Minä haluan ostaa lippuja. Thanks,
Why is it that with the same verb variations to the noun are possible? This is a question that one could write a doctoral thesis on, and actually, many have. I'll try my very best not to.
You already gave the short answer yourself: with a verb like ostaa 'to buy', we need to look at the thing that we're buying. If it's countable, we use the genetive, just like in your example: Ostaako Peter bussilipun. If it's not countable, or in Finnish, an ainesana, then you use the partitive.
Ainesanas are things that you can't count: food, drink, elements and abstract things, like
vesi, tuli, rakkaus 'water, fire and love'.
Just like you said in your letter, ainesanas can be conceptualized as countables: instead of milk, which is an ainesana or uncountable, we can talk about cartons of milk and transform our milk into countable form:
Ostan maitoa. 'I'm buying milk'
Ostan maidon. 'I'm buying a carton of milk.'
The same goes for jäätelö, and any ainesana for that matter. From you're letter, I'm guessing that you're thinking about individual ice creams. Think of big batches of gelato instead, or tubs of Ben & Jerry's.
Ostan jäätelöä. 'I'm buying ice cream.'
Ostan jäätelön. 'I'm buying an ice cream.'
On a more general level, how do you choose the case?
When you're first starting to study Finnish, the way we use our 15 cases may seem completely random and very confusing, but there's actually a method behind what may at times seem like madness. It has everything to do with the action you're describing, or, the verb you're using.
Some verbs go strictly with one case, like tykätä 'to like'. Tykätä always goes with the elative case (Mistä?):
Minä tykkään sinusta.
Minä tykkää-n sinu-sta.
First there's the word minä 'I', in its nominative or basic form, then the verb tykätä 'to like' in the form that goes with minä, the first person singular: tykkään 'I like'. Then sinä 'you' in the elative form, sinusta. So literally: I like "from you", or my liking of you comes from the way you are. I like you.
Other verbs are more flexible, like the verb ostaa that we started off with. Ostaa is a transitive verb, a verb that typically takes an object: you always buy something, and what case you should use depends on the thing you're buying: ainesana or not? If you're not buying anything in particular, there's a whole different verb for that: shoppailla.
So, you might saying, it's another f***** learn it by heart situation isn't it???
Well, you're right, it is. On the other hand, it's also not - when you progress further, you'll start to grasp the underlying logic, and you'll start to see that verbs with similar meanings behave in the same way. For example, this thing about liking from may seem totally random at first, but when you learn more verbs you start seeing a pattern:
'I like chocolate.'
'I like chocolate.' (pidän and tykkään are synonyms)
'I enjoy chocolate.'
'I dream of chocolate.'
In my opinion, the trick in the beginning is learning slightly longer chunks of language. Instead of memorizing tykätä + elatiivi, use it in a a longer sentence or phrase and then memorize that. If you love chocolate like I do, it could be tykkään suklaasta.
Once you know how to say you like chocolate, you also know how to say you like other things:
tykkään Helsingistä (Helsinki : Helsingistä)
... and so on.