 In his Logic, Condillac illustrated this point by asking his readers to imagine a group of people who travel by night to a chateau situated on a high point before a vast panorama of fields, mountains, cities, towns, and forests. At dawn, the windows are thrown open for just an instant. In that instant, each member of the company experiences a compound visual sensation consisting of multiple, simultaneously present colour patches disposed in space so as to depict all the parts of the panorama that lies out in a particular direction. But from the view obtained in just an instant, no one can say what it was that they saw. If the shutters are left open for more than an instant nothing new is presented to the company. That is, they do not have any sensation they did not have in the first instant. They come to perceive what it is they at first already sensed by selectively attending to each of its parts in turn and then noting how these parts are related to one another (Logic, Part I, Chapter ii).