you can understand just with practise . Examples : yap(ma) , sev(me) , gel(me) generally "ma , me " give NEGATIVE meaning. burada uyuma. = dont sleep here. but sometimes "ma ,me " suffixes dont give negative meaning that time these suffixes show you NOUN . Hayat sevme sanatıdır. and "iş" generally add after verbs and these verbs change noun versions. gidiş , kalış ,uçuş all of them are noun but "gitmek kalmak uçmak " these are verb. be carefull and english is same -ing sometimes change verbs for noun versions and "iş ış uş üş " like " -ing " mak mek always show us actions .so generally just for verbs in short " ma me " generally for negative meaning , "iş ış üş " make verbs noun and "mak mek " generally for verbs suffix

Good question. Even I don't know how to answer this. I think there is no certain rule. I will think about it. I can only say they sometimes may sound odd when used interchangeably. Sorry.

I suggest you not to focus heavily on the grammatical details. You can get the hang of it over time... Most foreign people make small mistakes especially when using suffixes, but we easily understand them. If you happen to say "gitmak", few people would even bother to correct you :)

thanks anarcotaurus but it is not a good news for one who wants to study Turkish. I want a rule :)

If you are intending to use these suffixes in single words, they are interchangable - and yes, they convert verb into noun. Whereas in any sentence, you have to use -mek, -mak suffix to convey "to do something" For example: "gitmek istiyorum (I want to go)" You can't say "gidiş istiyorum" or "gitme istiyorum" How about "-me,-ma" or "-iş,ış,uş,üş"? Take a look at those examples: "gidişimiz uzun sürdü" or "gitmemiz uzun sürdü" That means "it took a long time for us to go" Since the main verb is "to take" in the example, we no longer use "mak" suffix. Another point: we can say "gidiş uzun sürdü", but we can't say "gitme uzun sürdü" I'll defer to grammar experts to provide better explanations, but I think a flawless turkish can only be acquired through experience. As a native speaker, I find turkish to be a chaotic language with so many exceptions when it comes down to details.