This thread from Abla was about the use of question words paired with conditional -sem to convey whatever, whenever, etc. 

I had asked a question on that thread about the differences in context for "whenever" on whether to use Ne zaman or the -dik particle. And my question was overlooked, but no problem. I have not been so active recently.

Another question I have about it. If -sem with a verbstem can make a statement optative such as "Bugün tatil olsa" - I wish today was a holiday. Was Prof. Lewis correct on this?

How is it different than conditional? Where the clause is placed or if its the main clause? For example the hypothetical(conditional) situation:

"If today was a holiday, I would be swimming now"

Prof. Lewis is right. If the sentence had proceeded [compound verb] as below ;

Bugün tatil olsaydı     yüzmeye giderdim.

-----------------        ---------------

If today was holiday     I would go for swimming.

-------------------     ----------------------

Subclause            of        Main clause

Adverbial clause    of      main  clause

Conditional clause   of     main clause

as  the question is ´in what case ´ [in what condition] we would go for swimming ?

answer is"´in the case of today being holiday  "[in the condition of today being holiday]

------------------------------------------------

If you want to keep the optativeness in compound sentence then we should change the sentence into something like this ;

Bugün tatil olsa da yüzmeye gitsem. --> I wish  it was holiday today so that I could go for swimming.

In other words "I am wishing today being holiday and I am wishing to be able to go for swimming as a result of it as well.

I also visited Ne yapsam again yesterday. It is a pearl among threads. I recommend.

As ever, thanks Tunci. 

I love that there is so much extra aspects explained here by both the great tutors and other learners, than even in the grammar books. I´ll just have to practice so I remember the different contexts of "whenever" and "however".