As you noted, all four mean "difference" as nouns, and "differentiate" as verbs. Of the four, 區別 is the most neutral term. It simply means to "differentiate" without making any value judgment. So you can say 要區別中文和韓文字，只要看文字裏有沒有圓圈圈。 Because of the word 差literally means "inferior," a slight value judgment can creep in when using 差別。So racial discrimination can be written as 種族差別得遇，but not really 種族區別待遇。In casual everyday use, however, the two terms are used interchangeably, except in "fixed expressions." Even in English we cannot always substitute a synonym in a fixed expression. (He's on "cloud nine." But not he's on "cumulus nine.") Because of the word 距 literally means "distance," when using this term to compare things, you have to have some sense of "distance," either tangible or metaphorical. So you would say 他所保證的，和他所做得到的，有一段差距。(not 差異) There is a difference between what he promises and what he is able to do.

So I won't discuss the common meanings of the four words. Instead, let's analyze the difference directly. Let's mark two objects as A and B. 区别 is mainly used in the comparison which differentiate A and B; and it can be used as a verb. what 区别 do they have? How can I 区别 A and B? 差别 is mainly used to highlight the difference of the shapes, structures, or contents between A and B. The only 差别 between these two iPhones is that they are made in different countries. They are both designed by Apple. 差距 is mainly used between abstract things, like levels or standards. And it highlights the distance. My English skills have great 差距 with you. The quality of LG mobile still has 差距 from Apple. 差异 is mainly used for difference of essence and nature. The cultures between China and Australia have 差异. Hope it helps.

【区别】 区别的意思重点在【别】， 也就是你找到要区别的两个事物的差异，是为了辨认他们，标识他们，把他们作为不同的事物来对待。 另外【区别】可以做动词 “你要把它们区别开” You should differ them clearly. 【差距】这个词用在对“某种性质”上的比较。 这辆车和那辆车（性能上）有差距。 我说英语和你（水平上）有差距。 农村和城市（基础设施）有差距。

Sir, 道区别，distinguishing 差别，difference 差距 gap, disparity 差异的(of) ’差异 difference 英文線上字典,包含英漢字典 ( Chinese to English dictionary) http://cdict.net/?q=%E9%81%93%E5%8C%BA%E5%88%AB This dictionary will decrease your questions.s..s.. in Chinese . ha(^-^) Everyone can take a rest of Chinese explaination, sire.

I‘m agree with Venn ，but i think the little difference between '差别'and'差异' is，they always use in different idiom,you can say ‘差别待遇’but you can't say‘差异待遇’