International Encyclopedia of Systems and Cybernetics

Forecast and planning are possible at different time horizons.

Short term forecasts are needed for immediate action, but their results are useful at medium and at long term only if correlated to these last, since short term action must be non-contradictory with medium and long term trends.

These last produce the needed directive correlations, but would also be useless if not providing a satisfactory setting for short term forecasting and action.

M.P. SCHUTZENBERGER gives an example of this, which he relates to so-called "spans of foresight": "If the man coming down the hill plans each next move according to the details of the next hundred feet he will do better than if he were to plan only over the next ten feet. The spans of foresight are here a hundred feet and ten feet respectively" (1969, p.210).

Of course, planning for the next hundred feet is efficient only if a sufficient knowledge exists of what is going to happen within the next ten feet and if a satisfactory integration of both forecasts can be obtained.

In any case, forecast should be taken with some skepticism, since we never know the whole of a situation, nor all the complexities of the dynamics of its possible transformations. As stated by G. PASK: "… we are not predicting events, but certain abstract entities called the probabilities of events which can be variously interpreted" (1961 , p.19).

Moreover forecast is widely different from prediction, which is obtained in a scientific sense through the application of strictly deterministic dynamics laws to some classes of natural phenomena, as for example eclipses.