To what extent is socialism a coherent doctrine?

The emphasis of the question must be borne throughout any answer, notably "extent" (which requires any conclusion to consider the degree of difference) and "coherent" (a term which has a connotation of normative judgement as opposed to unified or singular for instance.)A good answer would both outline distinct ideological forms within the tradition of socialism, and reflect and compare on the degree of their compatibility. To make the essay manageable I would suggest dividing an answer into three obviously distinct traditions. The first parliamentary socialism, the second revolutionary socialism, and the third "Third-Way socialism" which are sufficiently variant so as to be able to show the skills of comparison and evaluation. A neat structuring would be :1.) Outline the commonalities between the three: the belief in some notion of fundamental equality, public ownership, and a criticism of capitalism, above all 2.) Address parliamentary democracy's origin as being distinct historically, because of the vote not existing at the time of Marx's writing or earlier socialist writers, but also explain that it won the support of all socialists at the time. 3.) Begin the second section by outlining revolutionary socialism's critique of parliamentary process as "bourgeois" , or a "committee for managing the affairs of the ruling classes" (Marx), but then point out that revolutionary groups have used parliamentary means at times. 4.) Begin the third section by outlining "Third-Way" socialism's criticism of both other traditions as belonging to the past, and its offer of a socialism for the present period's consensus on liberal democracy and regulated capitalism, but also describe how it has transformed the notion of equality, and public ownership that both other groups were committed to. To give contextual strength to this argument, historical examples of both the incoherence of differing schools of socialist thought (for instance the Mensheviks and the Bolsheviks in the Russian Civil War) and unity, for instance the opposition of all socialist traditions to the radical freemarket economics of Thatcher and Reagan in the 70s. Conclude by weighing the initial differences against the criticisms the schools offer of each other.