Naïf - pronunciation
Words based on the French naif, naive, naiveté can confuse speakers of English by the way they are said, and the related way in which they are written. The use of the diaeresis ¨ over the '-i-' is a feature of the French way of writing the words. It indicates that the '-a-' and the '-i-' are pronounced separately, as two different vowels, not as one diphthong - 'nah-eev' IPA: /nɑː (or aɪ) iːf/ and IPA: /nɑː (or aɪ) ˈiːv/, not '
nafe' and ' nave' IPA: /neɪf/ and IPA: /neɪv/ or even as ' knife' IPA: /naɪf/ . Many English writers ignore the diaeresis, and OED gives naif, naive and naivety as alternative forms. If you want to show yourself as a traditional academic writer, with some old-fashioned elements in your style, you are advised to use the French forms.
Note that in English, where gender is not as important as in French, the feminine form naive can always be used. Some readers may feel that to use naif (the masculine form) is 'precious', affected or plain ostentatious (showing off). You will never be wrong in English to stick to naive (or naïve, of course).
The abstract noun, the "quality of being naïve", is naïveté. Again, the diacritic mark, the acute accent (´) over the final '-e' (é) is there to show that the letter is pronounced (in French). The result is that it sounds, in English mouths at any rate, just like the pronunciation indicated by the more English spelling naivety.