the {-nIS}, expresses "need"; it isn't equivalent with the english "must".

if I write {jIQongnIS}, then this means "I need to sleep". I need to sleep because I am exhausted. Similarly {jISopnIS}, is "I need to eat"; I *need* to eat, because I'm starving.

But what if I want to express "must" ? The must doesn't necessarily express "need". Mainly it expresses "obligation". Mainly it expresses "necessity".

So, I thought that perhaps in order to express the "must", we could use the {'ut}.

Example: "because you're a bad cat, I must tickle you" {vIghro' mIgh SoHmo' vIqotlh. 'ut.}

Here's a better way: vIghro' qab SoHmo' qaqotlh net raD because you are a bad cat, I am compelled to tickle you.

However there is a problem. In the above example, while the english sentence describes a necessity to perform an action in the future (near or not so near), the klingon one doesn't. It says "because you're a bad cat I tickle you. it is necessary".

So, in order to get the job done, we only need to place a {tugh} in the beginning, or any other appropriate time stamp and we're good to go.

Your Klingon example does not express past, present, or future, so one does not necessarily expect it to mean that you'll tickle the cat RIGHT NOW. You're just being vague. Your time-stamp solution is making the situation specific.

My use of net raD is not the One True Way of translating must, but it often does a good job.

-- 
SuStel
http://trimboli.name