Wave energy converters (WECs) based on oscillating bodies or oscillating water columns would earn huge benefits from a time-domain control on a wave by wave basis. Such a control would allow efficient energy extraction over a wider range of frequencies than what could possibly be achieved when no real-time control is adopted, thus increasing the economical attractiveness of the WECs. Almost every control strategy that showed some potential, however, sffers from the problem that future knowledge of the incident wave elevation, or wave excitation force, is required. In this paper a general control framework for oscillating WECs is presented and a methodology to understand and quantify the wave excitation force prediction requirements, along with the achievable prediction accuracy, is discussed. The two features are compared against each other and linked to the dynamic characteristics of a device. Along with the qualitative discussion, the methodology is applied to some heaving cylinders when reactive control and linear passive control are applied, under different sea conditions.