I'm a beginner in English syntax. Some of the terminology used in papers by generative grammarians is very hard to follow. This is one case. As can be seen from the picture, the author says that "the need to check [+Ref] at D". So can anyone help me? I will be very grateful for that. Moreover, is there any glossary that contains all the terminology used in generative grammar in which I can understand these abbreviations? Also, what are your suggestions when you try to read an article in generative syntax but don't have so much background information in that area?