What does it mean that prepositions are not inflected?
its form does not change. the only time the preposition changes its form is when it ends ina vowel and the following word begins with a vowel. the final vowel is dropped and marked with an apostrophe. this is called an ellision.
when a peposition ends in a vowel and the folowing word begins with a vowel and a rough breathing, the consonant before the vowel in the preposition often changes. meta + (h)nmwn = Meth' (h)nmwn.