Public investment in advanced economies is at historical lows, following a declining trend since the 1980s. Two main hypotheses have been posed to explain this evolution: (i) the ‘social dominance hypothesis’, whereby increased public social spending has been displacing investment from government’s budgets, despite the upward trend witnessed in tax burdens and debt; (ii) fiscal rules’ frameworks, that would have forced governments to reduce investment in their quest for compliance. In this paper, we jointly test the validity of these two duelling explanations using two empirical approaches (panel data models; local projections) for a sample of advanced economies comprising data for the past six decades. We find that both factors are relevant to explain the observed downward trend in investment, with social spending acting as a structural driver, whereas fiscal rules contributed mainly when applied in fiscal consolidation episodes.