The original strand. Key thinkers: Marx and Engels, Luxemburg. Socialism can be brought about only by the overthrow of the existing political and societal structures.
Humans are naturally sociable and cooperative, bound by common humanity, and shaped by the environment within society (Marx and Engels). But capitalism alienates people and damages human nature, so only abolishing capitalism can transform it (Marx and Engels, Luxemburg).
Under capitalism the state is an instrument of class rule. It must be smashed by revolution and replaced by a transitional workers' state that eventually withers away. No accommodation with capitalist democracy is possible because capitalism rests on exploitation (Luxemburg).
Capitalism must be abolished and replaced with common ownership of the means of production (Marx and Engels). The free market is corrosive; workers must own and control production. There is no way to humanise capitalism enough to make it just.
Equality must be absolute, not relative (Marx and Engels). A vastly unequal society is unfair, and only a classless society with common ownership delivers genuine equality - reducing inequality through redistribution is not enough.
Socialism comes only through the overthrow of existing structures. Reform alone will not work because it leaves the state's class character intact (Marx and Engels), and no accommodation with capitalist democracy is possible (Luxemburg).
Capitalism is based on an economic relationship of exploitation (Luxemburg) and cannot be humanised into something just. It produces inequality, alienation and class conflict, so it must be abolished, not reformed.
The evolutionary strand. Key thinkers: Webb, Crosland. It wishes to humanise capitalism in the interests of social justice. Revisionism (Crosland) is a description inside this strand, not a fourth strand.
Optimistic and rational, like revolutionary socialism: humans are naturally cooperative and shaped by their environment (Webb, Crosland). The difference is that capitalism only limits human nature; it does not need abolishing for people to thrive (Crosland).
The state is won peacefully at the ballot box and expanded, not overthrown. Its expansion, not its overthrow, delivers socialism - Webb's 'inevitability of gradualness'. Tools are welfare, progressive taxation, redistribution and nationalisation of key industries.
Capitalism is humanised rather than abolished. The result is a mixed economy - some industries nationalised, much of the private sector left in place (Crosland). Webb's nationalisation of key industries delivers partial common ownership without revolution.
Equality is relative, measured by outcomes through welfare and the redistribution of wealth (Crosland), not absolute. The state reduces inequality rather than eradicating it, so a thriving private sector is acceptable.
Power is achieved peacefully through the ballot box (Crosland), not revolution. Webb's 'inevitability of gradualness' captures the method: change is slow, peaceful and democratic, with the state used rather than smashed.
Capitalism can be made to serve socialist ends through state intervention, regulation, welfare and redistribution (Crosland). Markets are tools to be shaped by the state, not enemies to be destroyed, so capitalism is humanised rather than abolished.
The newest strand. Key thinker: Giddens. A middle-ground alternative route between socialism and free-market capitalism.
Less optimistic than the older strands. The Third Way gives more emphasis to how human nature can be problematic and to individuals taking greater responsibility for themselves and their community (Giddens), framed through communitarianism rather than common humanity.
The state is kept and used democratically, not smashed. It is modernised: its role is social investment in infrastructure, education and skills, not economic and social engineering (Giddens). The evolutionary route is shared with social democracy.
The free market is accepted in a way the older strands reject (Giddens). The Third Way has moved away from limiting private economic ownership, so common ownership of the means of production is not its aim.
Equality is reframed as equality of opportunity - equal life chances and social mobility - rather than equality of outcome (Giddens). Critics inside socialism argue this legitimises wide inequality.
The democratic, evolutionary route is kept, shared with social democracy (Giddens). Power is won at the ballot box; the Third Way rejects revolution as firmly as social democracy does.
Markets are accepted, even welcomed, as the most efficient way to allocate resources, with the state addressing market failures and protecting the vulnerable (Giddens). Capitalism is harnessed for social ends, not abolished or substantially redistributed.