We present two ways in which trading in a replicatable option can affect the price process of the underlying asset. In the first situation, trading an option that each investor views as pay off redundant breaks a non-fully revealing equilibrium that exists when the option market is absent. The second situation involves a market that is dynamically complete without options, but in which introducing an option market allows self-confirming conjectures of additional uncertainty about the future price of the underlying asset. Heterogeneous beliefs play important though different roles in both situations.

[We present two ways in which trading in a replicatable option can affect the price process of the underlying asset. In the first situation, trading an option that each investor views as payoff redundant breaks a non-fully revealing equilibrium that exists when the option market is absent. The second situation involves a market that is dynamically complete without options, but in which introducing an option market allows self-confirming conjectures of additional uncertainty about the future price of the underlying asset. Heterogeneous beliefs play important though different roles in both situations.]

We develop a multiperiod rational expectations model of securities market equilibrium in which equilibrium prices may move between periods even though it is common knowledge that no new information has arrived about ultimate security payoffs. This happens because investors know they have imperfect information about the endowments of other investors and this knowledge affects their probability beliefs about the prices that will prevail at the intermediate trading date. These beliefs are reflected in the equilibrium at the initial trading date when investors focus on the probabilities of intermediate capital gains and losses, rather than ultimate payoffs.

ABSTRACT We develop a multiperiod rational expectations model of securities market equilibrium in which equilibrium prices may move between periods even though it is common knowledge that no new information has arrived about ultimate security payoffs. This happens because investors know they have imperfect information about the endowments of other investors and this knowledge affects their probability beliefs about the prices that will prevail at the intermediate trading date. These beliefs are reflected in the equilibrium at the initial trading date when investors focus on the probabilities of intermediate capital gains and losses, rather than ultimate payoffs.