Breaking down the question
The instruction comment on a quoted proposition asks you to evaluate its truth, not merely explain it. The claim is that the open-closed distinction is a matter of degree, never of absolutes: no real society permits perfectly free movement, and none wholly forbids it. Establishing this requires defining the two ideal types and then showing that every actual stratification system falls somewhere between them.
How to approach it
Define an open system — mobility permitted, status achieved — and a closed system — mobility barred, status ascribed. Present class and caste as the classic illustrations. Then make the central argument: both are ideal types, and empirical reality is always a mixture. Show closure within open systems and mobility within closed ones. Sorokin and Srinivas supply the evidence. Ground the discussion in social mobility.
Model answer
A society is called open when its stratification permits ready movement between positions, statuses are achieved through individual effort, and barriers of birth are weak. It is called closed when movement is barred, statuses are ascribed by birth, and boundaries between strata are rigid and often ritually sanctioned. Class society is the model of the first; the caste system the model of the second.
The quotation's insight is that these are ideal types — analytical extremes against which real societies are measured — and no actual society reaches either pole. Consider first the supposedly closed. Even the caste order, among the most rigid systems known, permitted movement. M. N. Srinivas's concept of Sanskritisation showed how lower castes could raise their collective status over generations by emulating the practices of the twice-born, while positional change and regional variation belied the image of total fixity. Slavery and estate systems likewise had their manumissions and exceptions.
Now consider the supposedly open. Modern industrial class societies proclaim equality of opportunity and achieved status, yet mobility is far from unlimited. The inheritance of wealth, the transmission of cultural capital, differential access to education and networks of privilege all reproduce advantage across generations. Sociological studies of mobility consistently find that origins strongly shape destinations; the class structure is elastic but sticky. Ascriptive factors — race, gender, family background — continue to constrain movement even where law forbids formal barriers.
Pitirim Sorokin, in Social Mobility, argued that no society has ever been either completely closed, since some vertical circulation always occurs, or completely open, since some obstacles to movement always remain. Both features coexist in every society, varying only in degree and channel.
The proposition is therefore sound. Openness and closure are ends of a continuum. Every real stratification system combines avenues of mobility with mechanisms of closure; the sociological task is to measure how much of each, and through which channels, rather than to assign a society to one absolute category.
Examiner's perspective
Examiners reward candidates who read the quotation as a claim about degree and organise the answer around the ideal-type continuum. The decisive move is to demonstrate mobility within a closed system and closure within an open one — Sanskritisation on one side, the inheritance of cultural capital on the other.
Citing Sorokin's dictum that no society is wholly open or closed is almost mandatory here, and Srinivas grounds the argument in the Indian context. Weaker answers simply define open and closed systems and stop, never commenting on the proposition. The top band goes to a script that treats the two types as poles of a single continuum and supports the point with evidence.