The "partitive" form takes precedent above both genitive and basic form, meaning that if there is some reason to use partitive (for example the verb demands it, the sentence is negative, ... etc.) it is automatically used above these other forms. Next in line is usually genitive form (or one of the many other forms needed in different contexts!), which often leaves a Finnish learner wondering when (if ever!) does one use the basic form of words.
Here are some main examples:
1. Minulla on - "I have"
"I have" form in Finnish, doesn't demand partitive automatically, so if you want to say you have "one whole thing" - the basic form is used:
Minulla on auto. = I have a car.
But note, as soon as the sentence is negative - partitive is needed:
Minulla ei ole autoa. = I don't have a car.
2. Passive form
Any passive form (where we don't know who is doing the action) will use the basic form of the word, unless there is a good reason to use partitive, for example:
Koulussa luetaan kirja. = In school a book is read.
Note the difference for a sentence where we know who is doing the action:
Hän luki kirjan. = He read the book. (Now we need genitive to indicate he read the whole book).
And note that partitive is used when it's a negative sentence:
Kokouksessa ei tehty päätöstä. = A decision was not made in the meeting.
3. Imperative form
For the imperative form, where you are commanding someone to do something (go! do! stop!), the basic form is used:
Tee se! = Do it!
But again as soon as the sentence is negative we are back to using partitive:
Älä tee sitä! = Don't do it!
4. Onko mahdollista... [+ verb]
This last example is one I have noticed many times, but do not know the name of it as a "grammatical rule". Basically when you have the form "onko mahdollista" combined with a verb - you need to use basic form (NOT GENTITIVE):
Onko mahdollista saada se tänään? = Is it possible to get it today?
And if I am not mistaken this same rule applies for the "minun oli tarkoitus" form:
Minun oli tarkoitus kirjoittaa teksti äitiyden yhteiskunnallisesta merkityksestä tänään. = I had planned to write a text about the societal significance of motherhood today.
Final notes:
-Don't forget partitive always takes precedent: if there is a reason to use partitive it must be used even in the above cases. For example if you have "some" items:
Minulla on kirjoja. = I have some books.
Or if you are working with a partitive verb (example "odottaa" = to wait)
Odotetaan sitä. = Let's wait for it.
I hope this made some sense and ask me if you have questions!
