Is there any other way you can "wax" as you do when you "wax philosophical"?
The wax in the phrase "wax philosophical" is a pretty strange bird. Its wax is obviously not the ordinary definition of wax, which my dictionary summarizes as an "oily, water-resistant substance", a definition which also serves as a fair summary of other, closely related "waxes", as in earwax or beeswax.
Neither is, I think, the wax in "wax philosophical" referring to another sense of wax, as in to grow, and which I know best in reference to the Moon "waxing and waning"; it means, as best I know, that the Moon is shrinking and growing in size. So is waxing philosophical "growing philosophical"? Sounds pretty strange to me.
The truth is, I only know how to use this set phrase, and can't really break it down into its constituents. It seems fairly archaic; the philosophical isn't even in the standard canonical form of an adverb, with no ending "–ly". So I was wondering three things: What is the canonical definition of wax as its being used here? In what other ways can you wax? Finally, if wax is acting as a verb here, why is it philosophical, as an adjective, and not philosophically as an adverb?
Merriam-Webster gives sense 3 for 3wax:
3: to assume a (specified) characteristic, quality, or state : become <wax indignant> <wax poetic>”
COCA gives a nice list of adjectives that are used this way with the verb wax:
WAX ELOQUENT
WAX ENTHUSIASTIC
WAX EUPHORIC
WAX INDIGNANT
WAX LYRICAL
WAX NOSTALGIC
WAX PHILOSOPHIC
WAX PHILOSOPHICAL
WAX POETIC
WAX PROFESSIONAL
WAX RHAPSODIC
WAX SENTIMENTAL
When I saw this question, I thought of the phrase “wax poetic” before “wax philosophical”. Indeed, “poetic” occurs 88 times in the corpus with verb wax compared to just 30 for “philosophical”.
And of course there is the Sponge album and song “Wax Ecstatic”.
EDIT: Google N-gram usage data for wax + the above adjectives, with credit to hippietrail:
As I understand it, to wax means to grow: if you wax philosophical, you grow philosophical, which probably means you become philosophically-minded, at least for the moment, and you occupy yourself with philosophical thoughts.
This is the same construction as when you grow old: old and philosophical are best considered subject complements, which is why they are adjectives, not adverbs.
[Edited:] According to Etymonline.com, both come from the Proto-Germanic verb *wakhsan, "to increase, grow", which in turn comes from Proto-Indo-European *wegs-, an extended form of the base *aug-, "to increase". Other dictionaries render this form as *owegs- or *awegs-. It is related to augment, which has come to us through Latin augeo, "to increase", and to Greek auxô, also "to increase".
However, a Dutch etymological dictionary, De Vries (4rd edition, 1997, p. 819), is undecided about the etymology of the substance wax (Dutch was, which is indisputably cognate) and gives Proto-Germanic *wahsa as a possible origin, related to English weave. The Proto-Indo-European root would then be **weg-/we-, "weave".
The great Woordenboek der Nederlandse Taal (article Was (II) from 1988) mentions both origins and says the matter is still undecided. It notes that Latin cera, the substance wax, comes from the same root as Latin cresco, "to grow", which might support a parallel relation in Proto-Germanic; the substance wax would then be "what grows slowly", as the bees add to it incrementally (yes, increment comes from Latin cresco). Note that the Latin words are no cognates of our word: they come from PIE *ker-, "knead", the origin of our words ceramic (through Greek kerannumi, "to knead") and crescent (through Latin cresco).
However, adds the WNT, modern German has Wabe, "honeycomb", which comes from aforementioned PIE *we-, "weave", and may very well be related to the substance wax; in addition, Dutch sometimes had een(e) was ("a wax", as opposed to simply "wax") well into the 17th century, which might indicate that the word referred to the piece of wax that constitutes a honeycomb.
A German etymological dictionary, Köbler (1995), is very succinct, but appears to consider the PIE root *we- cognate to PIE *wegs-.
Well, for one thing, it seems archaic because, outside the lunar context, it is archaic. Other usages are ironic, poetic, or examples of Wardour Street English: "He waxed wroth, and spake with an angry oath." That sort of thing
Here's the definition from NOAD:
wax 2 verb [ intrans. ] (of the moon between new and full) have a progressively larger part of its visible surface illuminated, increasing its apparent size. • poetic/literary become larger or stronger : his anger waxed. • [with complement ] begin to speak or write about something in the specified manner : they waxed lyrical about the old days.
The etymology is OE weaxen via Germanic; similar to German wachsen (to grow). NOAD gives a slightly different etymology for the noun: OE wex, weax, Germanic origin, similar to German Wachs.