A consumption theory that posits individuals choose current consumption based on expected long-run average ('permanent') income rather than short-term fluctuations; transitory income changes are largely saved, while changes perceived as permanent shift consumption proportionally to the change in expected lifetime income.

Principle

Consumption responds primarily to revisions in expected permanent income; temporary (transitory) income shocks have smaller effects on consumption than equal-sized permanent shocks.

Demonstration

Illustrative scenario → Situation: A worker receives either a one-time $5,000 bonus or a permanent annual raise that increases expected lifetime income by an equivalent present value. → Recognition: Under the hypothesis, the worker treats the bonus as transitory and the raise as permanent. → Action: The worker saves most of the one-time bonus but increases ongoing consumption after the raise. → Consequence: Aggregate consumption rises more following the permanent raise than the one-off bonus.

Misapplication

Concluding the hypothesis holds for all households: it is often misapplied by ignoring liquidity constraints, borrowing limits, uncertainty, precautionary savings motives, or heterogeneity—conditions under which transitory income may be spent.

Consequence

Policy implication: temporary fiscal transfers or short-lived tax cuts typically stimulate consumption less than policies that change households' perceived permanent income; empirical magnitude depends on credit access, risk, and information.

Reversal

When a substantial fraction of consumers are liquidity-constrained, uninsured against income risk, or have high precautionary motives, transitory income can raise consumption immediately; therefore the PIH's prediction reverses in such populations.

Boundary

Clearly within: forward-looking, optimizing agents with access to smoothing via credit markets and stable expectations. Boundary case: agents with intermittent access to credit or partial information. Clearly outside: hand-to-mouth consumers who consume most current income.

Semantic Tension

Tension with Keynesian (current-income) consumption functions and with behavioral models emphasizing myopia, liquidity constraints or precautionary motives; empirical relevance is population- and context-dependent.

Synthesis

PIH reframes consumption as an intertemporal smoothing problem: its explanatory power depends on market completeness, information and risk; it thus predicts when income changes will alter consumption and when they will be absorbed into wealth rather than spending.