The word "purposivenesses" is a mouthful to say, but its spelling makes sense if you break it down phonetically. In IPA, it is spelled /ˈpɜrpəsɪvnəsɪz/. The "p" and "v" sounds are obvious, but there are a few tricky parts. The "r" is followed by a schwa sound, represented by the upside-down "e". The "s" at the end of "purposiveness" gets added to form the plural, and then the "es" ending signifies possession. Even though it looks complex, understanding IPA makes spelling words like this much easier.