What are thoughts, or propositions, exactly? I develop an answer to this question in relation to the Russellian and Fregean views – propositions as facts and propositions as contents –, defending a Kantian alternative: propositions as acts. I move from natural or naïve Russellianism and its difficulties to more sophisticated and promising Fregeanism, which can respond to these difficulties but only at the expense of leaving open serious explanatory gaps of its own. Along the way, I develop Kantianism as incorporating what is promising in Fregeanism while closing the gaps this view left open, and present it more systematically at the end.
