The tense of osagashi

Question

In the sentence "nanika osagashi desu ka?" (Are you looking for something), in which tense is "osagashi"? Why is it not osagashimasu?

Answer 1

“Osagasi” in this sentence is noun so it’s irrelevant to tense. I think the sentence is more like “Are you in search of something?” The verb in this sentence is “desu(ka)”, which is present tense.

Answer 2

First off: it seems that by "tense" you really mean conjugation - the complete set of changes (inflections) made to a verb in order to indicate tense (past/present/future), aspect (finished/ongoing/repeatedly occurring/etc.), mood (active/passive/hypothetical/command/etc.), etc. I don't think you are really confused about whether the sentence refers to past, present or future, but simply about why there is no "masu" ending.

The sentence does mean "Are you searching for something?" although of course the "you" is implied. (We could also suppose that the implied subject is, e.g., "the thing that you're doing".) In a hyper-literal translation - to show how the grammar works - we might say something like "do [you] exist in the state of searching for something?". It means this because "desu" is a copula (one of the functions that the verb "to be" has in English), and "osagashi" is essentially "searching" in a noun-like way (like, the state/condition of searching), thus "osagashi" + "desu" forms a verb that means something like "to be searching".

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In case you feel like digging in to way more gory details than are actually needed in order to understand it:

The verb [お]{o}[探]{saga}[す]{su} means to search for something¹ (the "o" is just an honorific here²), and [お]{o}[探]{saga}[し]{shi} is its i-stem, or "masu-stem". However, the i-stem is not a proper conjugation of a verb by itself. Rather, in general it's something more like a gerund (i.e., an abstract noun that describes some event) in English.³ This is noun-like, but has more limited uses than ordinary nouns.

Forms like this can go before [で]{de}[す]{su} - however, these cases don't work quite the same way (from an English perspective) as putting an ordinary noun before [で]{de}[す]{su}. [探]{saga}[し]{shi}[で]{de}[す]{su} isn't "is (equal to/an instance of) searching (the act, as an abstract concept)", but rather "is (exists) searching (a description of the current condition of the subject)".

This happens because Japanese doesn't really have a direct equivalent of the English "is" (which is highly ambiguous). [で]{de}[す]{su} is a contraction of [で]{de} (the particle) + [あ]{a}[り]{ri}[ま]{ma}[す]{su} (polite form of [あ]{a}[る]{ru}). That is, the underlying verb is really "to exist", and then we describe where or how the subject exists, using a で-marked indirect object. Alternately, we can say that this で is a connector that can convert a gerund (noun-like) into a gerundive⁴ (adjective/adverb-like) and then join it to the following verb.

We could instead attach the "masu" ending⁵ like you describe, and get roughly the same meaning. However, that then has to be the final verb; we can't put "desu" after that (it would be sort of like saying "are you be looking for something?").

_{¹In English, "to search for" is a phrasal verb; we think of the "for" as being part of the verb itself. When we "search" in English, the direct object is the place (especially a container) where we search, and the indirect object is what we hope to find. "for" functions as a marker for indirect objects, and in English we can't just skip direct objects for transitive verbs. However, "search for" lets us swap the objects around (and now we need something like "in" to mark a place for the search). The Japanese verb most commonly works like "search for", rather than like "search", although my dictionary suggests it can work both ways with a bit of finagling.}

_{²However, maybe you misheard a particle-を before the verb? There should be one, since [何]{nani}[か]{ka} is the direct object here - per the previous footnote.}

_{³In certain limited cases, this form also becomes a separate, ordinary noun - for example [呼]{よ}び meaning "call" as a noun (an invitation, act of calling, etc.) derived from 呼ぶ (the verb "to call"). Anyway, I don't want to say that it actually is a gerund, because European grammatical terms were designed for European languages.}

_{⁴Again, this is an approximation; I don't want to assert that it's correct to use terms like this.}

_{⁵Getting really pedantic, [ま]{ma}[す]{su} (or sometimes [い]{i}[ま]{ma}[す]{su}) isn't a "conjugation" in the way that "-ing" or "-ed" is in English; it's an actual auxiliary verb. In modern Japanese it would basically never be used on its own, but it commonly gets attached to i-stems of other verbs. The reason we don't use [で]{de} here is because the meaning of the verb is more like "do" than "exist", so we modify it with a description of what is done rather than how. This is similar to how "suru verbs" work.}