useful joining words

but

because

or

and

mais

parce que

ou

et

When to use

The two parts of the sentence don't match - one is positive and the other negative.

je déteste les sciences mais j'aime les maths

​mais but

Both parts of the sentence need to match - both positive or both negative.

j'adore les sciences et j'aime les maths

​et and

When to use

Two sentences - one opinion and one reason.

je déteste les sciences parce que c'est nul

​parce que because

Both parts of the sentence need to match - both positive or both negative.

Tu aimes les sciences ou les maths?

ou or