Stephen Hughes wrote:
If you are wanting to prefix an alpha-privative to the beginning of a word itself beginning with a vowel, there is a high likelihood that the form of the alpha-privative will be ὰν-. Depending on how you think about it or postulate an argument to explain it, the ἀ-/ἀν- could be described as adding (or dropping) the ν before a vowel (or before a consonant), or as deriving from a nasalised vowel "ạ", which resolves into either an ἀ- or an ἀν- depending on whether the word it was prefixed to begins with (or previously began with) a consonant or a vowel. The word you ought to have been using, before getting the suggestion given, is a derivative of ἄνορθος "leaning", "not upright". An example of a word where the alpha-privative before a vowel is written without the ν is ἀόρατος -ον "unseen".
You allude to the reason above. Historically, there was a digamma, so that the root was ϝορ-. Remembering what words began with a digamma originally is also important for doing proper scansion in Homeric Greek...
Is the "h" itself (cf. ὁρᾶν) strong enough to require the ἀ- form of the alpha-privative, rather than the ἀν-?