Japanese sentence not ending with a verb

[Delodephius]

So today I came across a sentence in the Assimil Japanese course, lesson 31, where I noticed that it does not end with a verb, like all the other sentences always have so far, unless they were just interjections. I understand Japanese is mostly SOV or OSV, so this sentence confused me. It goes:

それと三枚目にはその横にある白いタオルはいかが。
And for the third towel, how about that white towel there on the side?

I have this feeling there should be more at the end, like ですか/だ か, shouldn't it? The notes don't say anything, and I haven't delved into any books on Japanese grammar, just one about how to use particles, and a poster with all the possible suffixes for verbs.

[vonPeterhof]

It's pretty common for interrogatives to end sentences in plain speech (that is, without です／ます). だか wouldn't actually fit in this case, since です and だ aren't always interchangeable. Tae Kim explains it pretty succinctly; scroll down to near the bottom, to the headline "「です」 is NOT the same as 「だ」". I'm pretty sure that the only time だ can be used with か is in relative clauses, as also discussed in the linked page. It can be used in questions, but that makes them sound more like either statements of exasperation (あれはいったい何だ - What in the world is that!?) or rhetorical questions displaying a bit of an attitude (あのタオルはどうだ - How's THAT for a towel, eh?). And I'm pretty sure that いかが wouldn't really fit in either of those cases, since it's way too polite for that.

There are lots of other examples of sentences that don't end with something that can conventionally be described as a verb. Perhaps the most logical example would be sentences ending in i-adjectives, since those have a bit of a grammatical overlap with verbs in Japanese (Korean takes this even further in that there's basically no morphological distinction between verbs and adjectives). Since most adverbs are essentially forms of adjectives, and since most interrogatives can be analysed as either adjectives or adverbs (the latter is how Rikaisama categorizes いかが), I guess they are also in that boat. Aside from cases of such "faux verbs" and omitted copulas there's also colloquial sentences with the topic-comment structure reversed (なんですか、それ？), or with the topic reiterated for emphasis (ご飯食べましょうよ、ご飯！). These are often explained away by analysing them as two separate sentences, with the second one clarifying or strengthening the first one. I guess word order categorizations like SOV or SVO are a useful tool, but they don't always fully reflect all the nuances of usage in a particular language.

[Delodephius]

Thanks for that link to Tae Kim's site! I bookmarked it and will read through it.

Ok, I understand. だ is used for making statements, so it cannot be used in an interrogative sentence, while です is a polite form of "to be", and can be used in any case. Roughly.

I'm still trying to wrap my head around adjectives and verbs being more alike in Japanese than in Slavic languages (I know English, but I never learned grammar separately, but I have Serbian and Slovak), where adjectives and nouns are more alike, in fact in Serbian an adjective can be used as a noun without any modification to it. It will take time to get used to this idea.