Four months after parliamentary elections, formal coalition talks begin Friday between Germany's conservatives — Angela Merkel's Christian Democratic Union (CDU) and its Bavarian sister party the Christian Social Union (CSU) — and the center-left Social Democratic Party (SPD).

Merkel has said that she wants to conclude the negotiations by February 12. In 2013, the formal coalition talks for the current partnership with the SPD took three weeks.

It is, however, likely that the talks will not be plain sailing, with leftists in the SPD already voicing anger at a number of agreements struck in preliminary talks, especially with regard to income tax, family reunifications for refugees and health insurance.

Read more: The major sticking points in Germany's upcoming coalition talks

SPD members to vote on outcome

The full 440,000-strong SPD membership has been promised a say at the conclusion of negotiations as to whether they accept the coalition contract that has been drawn up. And that vote is anything but certain in view of the divisions within the party with regard to the inevitable concessions that will have to be made. Delegates voted in favor of starting talks in a close poll on Sunday.

Read more: Germany's SPD sees spike in applicants ahead of coalition talks

In addition,  many SPD members are of the opinion that another four years in governing partnership with the CDU and CSU could spell the end of any real individuality for the left-leaning SPD. The SPD has already been the junior partner in two "grand coalitions" with Merkel's conservatives, from 2005 to 2009 and from 2013 onward.

The next four years?

If they are successful and Merkel receives the necessary absolute majority in the Bundestag to retain her position as chancellor, she could possibly begin her fourth term in office before Easter.

That would mean that half a year had elapsed since the elections — the longest period that Germany has ever remained without a working government.

The September election saw both the CDU-CSU bloc and the SPD plummet to their lowest point since 1949, amid a surge in support for the right-wing populist Alternative for Germany (AfD). The attempt to form a grand coalition succeeds, the AfD would become the Bundestag's strongest opposition force.

Back to the polling booths?

The prospect of new elections if a coalition fails to come about may well deter those within the SPD who might otherwise make a stand on principles, with many worried that this could give far-right elements a chance to increase their foothold.