A concept is an idea that attempts to join together several observations. For exmaple, we observe that today the sun is shining, the temperature of the air around us is pleasant and we remember that we observed the same phenomenon yesterday, but the day before that it was cloudy, cool and damp. We notice that the plate that is holding our sandwich is very warm but the grass under our feet is pleasant. We might arrive at the concept that sunlight is a form of heat energy. We might test this concept by shielding some area and notice that the area is cooler. By adding other observations we expand the concept and perhaps even develop a theory about how all these observations are connected. Thus, we say the concept developed.