Is it incorrect not to decline "in" and "von" in dativ?

Question

I know both "von" and "in" are dative (in can also be accusative) prepositions and when there is an article either masculine or neutral, they are declined to "vom" and "im". Normally, when I speak German I say "von dem" and "in dem" without realizing it. Is this declination grammatically mandatory? Or is it correct when someone like me says "von dem" or "in dem"?

Answer 1

Hello,

Vom and im are contractions. That means a preposition together with a definite article. For example vom - von dem, im - in dem, übers - über das.

You can use both. Both are correct. Since the contraction is shorter, it is probably used more often.