Wicker808 wrote:The prefix may change the meaning of the verb.
Exactly, but the change isn't necesarily radical, e. g. when adding a directional prefix to a verb of movement.
Wicker808 wrote:The prefix will change the aspect of the verb from imperfective to perfective. If the verb is conjugated for present tense, this has the secondary effect of making the verb effectively future tense.
Yes, that's true.
Wicker808 wrote:Is it correct to assume that all verbs have a perfective equivelent with unchanged meaning formed with the prefix "meg"? Or, is it necessary in Hungarian, as in the Slavic languages, to memorize both the perfective and imperfective forms of each verb?
Unfortunately it is the latter, also adding that not every verb has both aspects. Besides, aspect (actually a bit more than that) might be denoted by affixes as well instead of prefixes:
villan - it is currently flashing (emitting light)
megvillan - flashes once
villog - it keeps flashing (it has no perfective pair)
világít - it is continuously emitting light (no perfective pair either)
As for non-meg perfectives:
olvas - elolvas, kiolvas (I can't really describe the difference in English, but the latter somehow puts more stress on the from-beginning-to-end nature of reading)
megy - elmegy
intéz - elintéz (gets something done)
ad - odaad (this is the prefix that doesn't change the essential meaning of the verb, as opposed to elad, megad, kiad etc. that are completely different)
And so on.
Actually, even the perfective forms can be made continuous by reversing the order of the prefix and the stem:
Most megy el a tanár. - The teacher is just setting off.
This also answers your second question I guess.
Wicker808 wrote:Are there are unprefixed Hungarian verbs which are nevertheless perfective?
Yes, those where perfectiveness is denoted by an affix.
Wicker808 wrote:Are there prefixed Hungarian verbs which are nevertheless imperfective?
I can't think of really nice examples here, but I must note that the aspect can also be neutral.
Wicker808 wrote:If the answer to either of these questions is yes, is there any reliable way to determine the aspect of a verb?
Not really. Time information is embedded into the vocabulary, so you have to learn them as separate dictionary entries.
Wicker808 wrote:Is it ever acceptable to use the "fog" future auxilliary verb with a perfective infinitive?
If you are alluding to Slavic aspect here, that's a sidetrack. In Hungarian you can use 'fog' with any verb, but there's rarely any need to use it. If you say e. g. 'el fogok menni', the auxiliary adds rather certainty than future, since the future was already there in the first place.
I have to go now, but keep asking anyway.