Questions & Answers about Yksi miljoona euroa olisi mahtava yllätys.
How do we form olisi in this sentence?
It comes from the verb olla (to be). We take the stem ol- and add the conditional marker -isi- to mean "would be". Because the subject is acting as a single thing, it uses the 3rd-person singular form, which has no extra personal ending after the -isi-.
Why is the word euroa in the partitive case here?
In Finnish, any number other than exactly "one" requires the following noun to be in the partitive case. Even though the sentence starts with yksi (one), the number counting the euros is miljoona (a million), so euro becomes euroa.
Why does the verb olisi use the singular "it" form when we are talking about a million euros?
When a number phrase like yksi miljoona euroa acts as the subject of a sentence, Finnish treats it grammatically as a single unit. Because of this, the verb takes the 3rd-person singular form (olisi) instead of a plural form.
Why are mahtava and yllätys in their basic forms and not in the partitive?
In "A is B" sentences, if you are describing a single, countable thing, you use the basic nominative form. Because "a surprise" is considered one whole concept here, both the adjective mahtava and the noun yllätys stay in their basic forms.