Abbas,Erekat and Palestinians in general are not setting pre conditions of any kind. They are asking Israel to abide by and comply with its committments and obligations under International Law and its previous signed agreements. To itemize....Israel signed the Fourth Geneva Convention making settlements illegal and aquisition of territory by war inadmissible.....Israel signed agreement to the Road Map agreeing to freeze all settlement construction including Natural Growth in accordance with the Mitchell Report........Israel agreed to implement Resolution 194 in exchange for full membership of the UN. When Israel undertakes its responsibilities under Law then negotiations can begin. If Israel does not negotiate and accept the Arab Initiative based not on Israels legal borders of 1948 but 67 borders then Israel will be responsible for the outcome of a One State Solution and the end of the Jewish State of Israel. If Israel wants to survive as a Jewish state under Two State Solution then it must honour its legal requirements...full stop.
Shaffir to Herzog: Opposition failed to show leadership in political battles against PM (Haaretz)
from the article: An open letter to Mahmoud Abbas: Save the two-state solution