Learn Swedish: Vi bygger inte teorin på falska antaganden. - We do not build the theory on false assumptions.

Antagande (assumption) is an ett-word that ends in a vowel. Nouns ending in -ande or -ende that describe an abstract concept or action belong to noun group 4. To make them plural, you just add an -n, so ett antagande becomes antaganden (assumptions).

Why does it say falska instead of falsk or falskt?

Because adjectives must agree with the noun they describe. Since antaganden is plural, the adjective takes its plural form, which adds an -a to the base word falsk.

What gender is teorin and how do we know?

It is an en-word (en teori). You can tell because its definite form (the theory) ends in -n, giving us teorin. If it were an ett-word, it would usually end in -t.

Why does inte come before teorin?

In a standard Swedish main clause, the negation inte goes immediately after the first verb. The structure here is Subject + Verb + inte + Object, which gives us Vi bygger inte teorin.