Using concise words like unsure for longer sentences

Question

Which is better English:

1. I am not entirely sure about this.
2. I am unsure.
3. I am unsure about this.

In the 2 and 3, using the word unsure has made the sentence relatively concise. However, is it always better to be concise? What about this case?

Answer 1

"Not entirely sure" infers that you are at least partially sure. Perhaps you are certain about some of the details of a whole matter under discussion, but not all.

By contrast, "unsure" really means that you are not sure. Idiomatically, it can often mean that you do just have some reservations, but if we were to grade your first two examples by how much surety they imply, this second example would suggest you are less sure.

Example 3 doesn't seem any different from example 2 - unless the wider context told us what 'this' is. If by 'this' you mean the entire matter under discussion, then there would be no difference. But you could use this to point to a particular aspect of the whole that you are unsure of - that would indicate that you were sure about most points, but not this particular part. In such a case, arguably this would be very similar to example 1 where you said that you were only partially sure/unsure.

It might be worth looking at the meanings of clear/unclear as well as certain/uncertain, as they carry slightly different inferences and could convey better what you are trying to say.

Answer 2

They're all fine in terms of English grammar. Whether they could differ in nuance, such that one was preferable to the others, is a matter of things like whether the words are to be spoken, or simply read; the intended level of formality; geographical region; and so on. For example, to me:

I am unsure...

is a bit more formal than:

I'm unsure...

or:

I am not sure...

Both of which are a bit more formal than:

I'm not sure...

All four are perfectly good English, but In normal, spoken conversation my preference would almost always be for the last of the them.

Also, even though milder uncertainty is clearly conveyed by:

I am not entirely sure...

I, for my part, would find "entirely" to be just a wee bit too formal in spoken English. Instead, I'd probably use something like:

I'm not totally sure...

In fact in practice I may even say the apparently stronger, "I'm not sure" (or even "I don't know" or "I dunno"), but use tone, facial expression, or body language, to soften it and add the nuance of actually being pretty sure but not certain. For example, imagine asking someone, "Are you confident in X?" And they reply:

"I'm not ... [pause, lips pursed] ... [holding the first "sh" sound longer than normal] sure"