Who Builds the Index Governs Capital
When a fund decides to replicate the S&P 500, it is not choosing which firms deserve investment. It is delegating that choice to the algorithm that composes the index. Those who construct and maintain the index acquire immense allocative power without formal assignment or democratic legitimacy.
Financial indices were created as instruments of measurement. They were meant to reflect the market, not orient it. Once passive management reaches sufficient scale, the distinction collapses. When most invested capital tracks the S&P 500, firms that enter the index receive automatic inflows of capital, while those that exit lose them. The index no longer measures the market. It determines it.
This is the performativity of financial models that MacKenzie (2006) analysed with precision: models do not describe markets. They transform them once they are adopted at sufficient scale. The same mechanism applies to indices. An instrument of observation becomes an instrument of governance.
Those who design the index decide which firms enter or exit, according to which criteria and which methodology. These decisions shape the global distribution of capital, sectoral development trajectories, and firms’ capacity to finance themselves. Yet they occur in technical form, within specialized committees, with public visibility close to zero.
The shift toward ESG indices in recent years makes this dynamic even clearer. When environmental, social, and governance criteria enter index construction, those who define those criteria acquire direct influence over which corporate behaviours gain access to capital and which do not. It is a form of private regulation of markets, exercised through technical instruments, without democratic mandate, with effects that no legislation could have produced with comparable speed.
Artificial intelligence is adding a further layer. Models that optimize index composition, identify inclusion criteria, and manage automatic rebalancing incorporate choices that were once explicit and now become opaque. The technician no longer decides. The model decides, and those who built the model have already determined what the model can see.