Users with more than 1250 reputation and a total answer score of 5 or more on the tag, can suggest tag synonyms. Users with a total answer score (total upvotes minus total downvotes) of 5 or more on the tag, can vote for tag synonyms.
It's clear that creation of tag synonyms is a very dangerous feature, but the restriction of “a total answer score of 5” for just making a mere suggestion seems a bit off.
Does this really reduce stupid suggestions in the case of philosophy.SE? You don't need an answer score of +5 on the proposed synonym tag, after all. (Of course this won't be changed, it's deeply embedded in the system).
EDIT: okay there's Zeno of Citium :-D