Translation:You are making a mistake.
The use of -taH here makes me flinch a bit about making "a" mistake. I tend to see this as a person who's habitually in error, not a one time thing (nor is it the same mistake over and over again). Moreover, this translation place more focus on the act or process of "making" a mistake, rather than the state of being mistaken. Just my cha' DeQmey.
Well, you know in movies where the high-ranking military guy wants to blow the aliens out of the sky, but the protagonist knows that'll just result in the rest of the aliens destroying the world? The protagonist usually bursts into the war-room and shouts "WAIT! YOU'RE MAKING A MISTAKE!" That's the sense I get. "ghobe'!!!! biQaghtaH!! tIQaw'be'!!"
Is -taH supposed to be more of a habitual meaning? The descriptions I've seen so far for -taH use the sort of wording ("continuous"/"continuing"/"ongoing"/"underway") that is used for grammatical constructions in other languages that can and often do refer to a single action, just one that is incomplete.
(Sometimes the two even seem like opposites...e.g. if a person is normally very brave but currently nervous, my attempt to express that would be yoH 'ach bIttaH. Should I instead say yoHtaH 'ach bIt? Or is there another aspect that would be more appropriate here?)
My take on the aspect suffixes is that they're as simple as the description in TKD - they indicate a temporal aspect of the action, without any of the additional complications that tense can add in other languages. Further, aspect suffixes are (almost) always optional, and the lack of one does NOT indicate anything at all.
For example, <bIghHa' retlhDaq jIQam> means "I am/was/will be standing by the jail" or "I stand/stood/will stand by the jail". <bIghHa' retlhDaq jIQamtaH> means pretty much the same thing, except that it emphasizes that for some period of time (probably clear from context), I was standing there the whole time.
There are a couple of complications - the suffix <-ta'> indicates not only aspect but intention. Also, the aspect suffix <-taH> is required with <-vIS>, while no aspect suffix is allowed with <-jaj> or in an <'e'>/<net> sentence as object construction, though all three of those rules have counterexamples in canon.
Back to the example - <bIQaghtaH> means "you're making a mistake (or multiple mistakes)", and also that the process of making that mistake is taking place over a period of time. And that's kind of weird in most contexts. If you make lots of mistakes, or are making a long, drawn-out mistake, it makes sense as something like "you continue to be in a state of error".
But for the normal English sense of "you're making a mistake", I would not use <-taH>.
the lack of one does NOT indicate anything at all.
Perhaps not always, but TKD says (§4.2.7) that
The absence of a Type 7 suffix usually means that the action is not completed and is not continuous (that is, it is not one of the things indicated by the Type 7 suffixes).
So "usually" it does indicate something, namely the fact that "the action ... is not continuous".
Unless there is something that came later that contradicts that part of TKD that I'm not aware of? (Quite possible.)
TKD says what it says, but we have an awful lot of canon examples of Klingon by this point, and a large majority of the verbs in those examples lack type seven suffixes. I don't take that to mean that the actions of the verbs in those sentences (usually) are not continuous or complete; I take it to mean that when there is no type seven suffix, the aspect (usually) doesn't matter.
Consider stative verbs (verbs which express a state or quality), for example. jIDoy'; bIyoH; Suval; etc. The action of those verbs (being in a state or expressing a quality) is continuous almost by definition - given the time context of the sentence, if I'm tired, it's a pretty good bet I will continue to be tired until I go to sleep, have a coffee, etc. But we very rarely see a -taH on a stative verb in canon (or elsewhere).
The actions of many active verbs - eating, walking, sleeping - are generally continuous as well. The action takes place without pause over some reasonably substantial period of time. But we don't usually see -taH or -lI' unless the aspect matters for some reason.
Given that Klingons value conciseness when speaking (Conversational Klingon, Power Klingon), I can't see their language requiring a full-syllable verb suffix every time I use a verb whose action is continuous, and the canon record backs me up.
Agree completely. Aspect in Klingon is NOT the same thing as tense in English. -taH does not automatically equate to the progressive.
The only ways I can think about bIQaghtaH that make sense are a person who is constantly, habitually in error, or someone in the process of making a very long, drawn out bad decision being advised time and again to change his mind.