Now that you are close to mastership of Euskara, let's talk about a grammar point that will enable you to better your sentences.
Just before, let me remind you of a small point we saw before:
Direct complement are often at the partitive case when the verb is negative:
Ez dut dirurik: I do not have money
Ez dut arrainik jan: I do not eat fish.
Keep this feature in mind for what's to come
1. YES, I think that...
Basque legendary stubborness requires you to be able to express what you think. To do so you need to know how to make subordinated clauses.
Let's begin by the beginning, i.e. some vocabulary:
to think / to believe: uste (meaning I think that, I believe that)
So: uste dut: I think (I've thought that, therefore I think)
Now the magic word: -ela. Like -en for a relative clause, ela is a postclitic, and merge like -en
We have to think the Basque way for clauses: ust like relative clauses or genitives, what determines is always put before.
I think that my friend has lost his keys:
would be in Euskara
My friend his keys lost has (that) think I
Nire lagunak bere giltzak galdu dituela uste dut.
I have forgotten that Peter do not undertand
A little syntax difference:
Ahazu dut Peterek ez duela ulertu.
2. NO, I do not think that...
Remember the refresh at the beginning
-ela becomes -enik, marked by the partitive
I do not think that my friend has lost his keys
Ez dut uste nire lagunak bere giltzak galdu dituenik.
3. Whether 'tis nobler for the mind to suffer...
Let's recall one old synthetic friend: jakin, to know.
I know you know but,...
Btw I know that you know: Dakizuela badakit !
Here we talk about indirect interrogative subordinated clauses.
I wonder whether...
I do not know whether...
As the answer requires yes or no, take the famous -en and add ez --> enez
I wonder whether he will come
Galdetzen dut etorriko duenez (as it has a "negative" meaning, the clause goes afterwards)
We'll see other indirect interrogative clauses later when we talk about interrogation.
Enough for today!