When you want to ask "Why?" in Turkish, is there a difference between saying "Neden?" or "Niye?"?

There is no difference between them. 

Neden, niçin, niye...they are all of same meaning

ANTS here, the altruistic native Turkish speaker,

With unnecessary explanations...

Neden = Ne + den = From what  (From what is this EFFECT taking its roots, reasons, CAUSES?)

Niçin = Ne + için = For what (used in english as well)

Niye = Ne + diye ~ So what (You did this, and this, so what? Why did you do that?)

You can see the connection between all three of them, right? They all kind of mean "why".

In English they all sound like they´d mean slightly different things but in Turkish, I can´t think of an example in which you cannot substitute one for another.

By the way, I haven´t read this in a book so it is not solid information but to a Turkish ear it is obvious.

Well, it´s obviously

niye (neye) = to what (goal/purpose) = why

I have a feeling that this sense of humour sounds familiar to me. Are you an old member with a new nickname?

I think so too but let´s see.

No I´m not.

You really must have missed that guy. Reminds me of Yılmaz Erdoğan´s "o da ekmek yerdi."

I thought he was "handsome". But I guess he is not He impressed me with his explanations about Turkish grammar and he hasnt written anything yet about Armenian genocide

The only reason I am not handsome is because I am very handsome. Very much above average. And speaking of Armenians, there´s this great etymological dictionary by an Armenian guy, which did not give any explanation for "niye". So I had to improvise.

http://nisanyansozluk.com/?k=niye&x=0&y=0

maybe vona/ scalpel  

They really miss me 

(this is just to save you from wrath of si++)

i heard villagers say: "ne diye geldin?" why did you come?

"ne diye" and "niçin" are same in meaning but niçin is common in cities while ne diye common in rural areas.

i dont know the origin of "niye"
"ne-ye": to what, seems logical when i look at the structure. at the same time "ne diye" is logical when i look at usage and meaning. i vote for ne diye.

Well, Before subscribing to semething blindly, just look at it again once more, it´s right there begging for you to see it!

That kind of phonetic change would leave traces in the past, can you provide any evidence to support that change you vote for?

At the first sight "niye" looks like it is formed from the question word "ne" with the suffix "-e/a" (ne+e = neye = niye) but "neye" still is there and in use. "neye" means "at/to what" whereas "niye" means "why". For example, "neye baktın?" means what did you look at?" and "niye baktın?" means "why did you look?" This is not to say TC´s official Turkish grammar expert dear si++ is wrong but just flame the discussion  

I don´t think ABL and DAT are so distant. What about

                    Neden korkuyorsun? Sevmekten.

                    Niye korkuyorsun? Sevmeye.

Both could be translated with ´why´.

I don´t believe in ne diye. It is a later abstraction. No phonetic erosion at all.

The grammaticalization path would be something like:

1. Neye bakıyorsun? (AT WHAT) > 2. *Neye korkuyorsun? > 3. Niye korkuyorsun? > 4. Niye bakıyorsun? (WHY)

1. Initial state, meaning 1.

2. Widened use with a limited set of verbs, meaning 1. and 2. side by side.

3. Phonetic change supports the semantic change, meaning 2.

4. Generalization of meaning 2.

(I am not sure if korkmak is the best possible example here but there must be a context where these two meanings lap together.)

I may be wrong. If I am wrong somebody should prove me wrong.

I don´t/can´t see any phonetic development like niye < ne diye. If there is any, let me know any related pointers/references.

alıntı:

according to someone

"Niye: Corruption of "neye", which is the dative of "ne". To what end?"
source: http://forum.wordreference.com/showthread.php?t=2653974&langid=20

according to someone else
"excatly niye is the short version of ´ ne diye ´ and they all exchangeable. niye,neden,niçin"
source: http://www.memrise.com/course/79355/hacking-turkish-1/thread/1305918/

"Niye" has an empty etymology space in Nişanyan Sözlük.

https://www.nisanyansozluk.com/?k=niye&lnk=1

It remains a mystery. I thought it was from neye, but I´ve been studying Turkish for just over a year so I am not very qualified to answer this.

DAt also used for indicating purpose or intented goal. From this point of view,in meaning, -a/-e is very close to "için": sevmeye = sevmek için (as in the example: sevmeye yürek gerek - sevmek için yürek gerek) So back to your example, "neye korkuyorsun - sevmeye" could also be "ne için korkuyorsun - sevmek için." 

I think it is:

-a/-e => için

neye => ne için

niye = niçin

p.s. you don´t have to thank me for my contribution here  

Nişanyan´s dictionary is not the only source actually. It is popular because it is online. I think TDK should work on this online dictionary issue.  If i will have chance to  check my etymology books i will let you now.  

But  now lets check from another point. 

In Turkey Turkish we are in doubt if  it is coming from ne-y-e or ne diye so let´s check some examples from other Turkic dialects, 

In Turkey Turkish        it is  niye    ne+e (dative)  / or /  ne + diye?

In Uzbek Turkish         it is  nega    ne+ga (dative)

In Kazakh Turkish        it is  неге (nege)   ne+ge (dative)

So above we can see one example from  each dialect group ( Oghuz, Qarluq, Kipchaq ). And according to the other dialect examples,  i think it is clear that niye is coming from ne+e. 

We are glad you are back at this god-forsaken website.

Hey,

I checked the dictionary (Türkiye Türkçesindeki Türkçe Sözcüklerin Köken Bilgisi Sözlüğü, Tuncer Gülensoy) and it is written like this;

neye ~ niye ´Bir olayın sebebini ve amacını sormak için kullanılır´

< ne [> i]+y+e