´Ãntihar edip etmediði hususundaysa hiçbir þey söylemem.´

I presume that this construct relays an uncertainty ie

´If on the subject of her commiting suicide there is some doubt I will say nothing.´

I have not come across this before and wondered, can we use it with all verbs and in all tenses.  For example could I say,

´Yarýn gelip gemeyeceksin bir pasta yapmacaðim.´  If you might not come tomorrow I won´t make a cake´.

I think you are missing something right here. If there is something more before this text you wrote, it means there is something and then, this sentence says "on the other hand" meaning with -sa/se suffix which is not "if".

Furthermore, your second sentence doesn´t have -sa/se suffix, this is another issue.

I think the correct explanation would be like this:

Ýyi bir insandý. Ýntihar edip etmediði hususundaysa hiçbir þey söyleyemem.

He was a good person. (On the other hand) I cannot say anything about the subject whether he commited suicide or not.

By looking at your English sentence (the second sentence you asked), I would translate it something like this into Turkish:

Yarýn gelmeyeceksen pasta yapmayayým

The other types of adding suffixes will be very fictious and not good, even though they might be ok for grammar.

"-ip -memek" type sentences are just for "wheter or not" relative clauses;

Gidip gitmeyeceðini bilmiyorum: I don´t know if/whether he will go or not

Your first sentence is a bit different by the adding of "ise/-se/sa"

Yarýn gelmeyeceksen, pasta yapmayacaðým.

As caliptrix said the "-(y)ip ... -ma" is a noun clause that expresses "whether or not" so you´d use it to say, for example, "whether or not you´re coming in tomorrow, I´ll make a cake".

The first verb stem takes on the -(y)ip suffix, whereas the second verb stem, after you add the negative -ma/-me, can take on a variety of suffixes, such as, for example: -dik, -y(acak), -ma, -mak, etc. 

You´ll see this usually as an object of verbs of "knowing" - bilmek, anlamak, fark etmek, etc., or also söylemek or sormak. In English those would be the type of expressions when you say: I don´t know whether or not s/he ...., I asked him whether or not ...., etc.

So the sentence that you wanted to use (with slight corrections): "Yarýn gelip gelmeyeceksin, bir pasta yapmayacaðim", would translate to "Whether or not you´re coming tomorrow, I´m not making a cake".

No, as I mentioned, you cannot build such a sentence in Turkish.

Hmmm, maybe I´m not understanding it as I thought I did

Is it because it´s a noun clause? How about this "Yarýn gelip gelmeyeceðini bilmiyorum, ama bir pasta yapmayacaðim"? Can you say that if you make this an object of a verb?

Can you say: Yarýn sen gelsen gelmesen de, bir pasta yapmayacaðim", to say "Wheather or not you come tomorrow, I´m not cooking the cake?".

Sorry to be a pain in the a* with the questions, I just want to make sure I understand it.

Thanks,

Ah, so it expresses an uncertainty and can be used in other tenses, so could I say

´O parayý çalýp çalmadýðý bimiyorum, ama artýk onu evimize davet etmeyeceðim´

´I don´t know whether she stole the money or not, but I will not invite her to our house again.´

And could I say,

´O parayý çalýp çalmamak bilmek istemiyorum, zaten onu hiç güvenmedim.´

´I don´t want to know whether she stole the money or not, I never trusted her anyway.´

And is this possible,

Hiç kimse bilemez ki bir adam sadýk olup olmayacak, ama evlenerken hepimis öyle duþunuyorus.

No one can know whether a man will be faithful or not but when we get married we think so.

Sorry to be a pain but it is bugging me.

Is the above a good rule of thumb?

Many thanks

I hope it helps.

Yes, you can say it.

No, you need a few corrections; O parayý çalýp çalmadýðýný bilmek istemiyorum, zaten ona hiç güvenmedim.

Correct one would be;

Hiç kimse bir adamýn sadýk olup olmadýðýný (or olmayacaðýný) bilemez ama evlenirken hepimiz böyle düþünürüz.

1. It might be acceptable maybe if it were just a normal sentence, but here you have to make the clause the relative clause of the sentence, you cannot join it by "ki" so easily with -ip -meyecek.

2. not hepimis it is hepimiz

3. düþünüyoruz > are you still thinking right now? I don´t think so, I think you will think when you need to think in a non-clear time in future. So you shouldn´t use -yor present continuous tense "þimdiki zaman", but you must use aorist tense "geniþ zaman".

4. ama doesn´t need a comma in Turkish generally even though "but" needs in English