The discovery of a creative solution occasionally corresponds to the sudden attainment of a
mental insight. Our purpose is to formally describe this phenomenon and the cognitive mechanisms
that lead to it. The approach is based on the replicability of just such an insight which
underlies the solution to a well known puzzle: the nine-dot puzzle. The insight coincides with
the realization that the problem can only be solved when a spurious constraint is removed. Two
experimental results are reported: one on the nine-dot puzzle and the other on an architectural
sketch design problem. The sketch design problem was structured with several restricting
frames of reference to create a situation analogous to the nine-dot puzzle. Subjects’ design
behavior was analyzed to identify the mechanisms used in achieving the mental insights which
allow designers to go beyond the implicit restrictions of these frames. A general model, called
SMI-GI, of the mental insight based design and discovery process is described. This model
foresees a computer system that can be used to simulate the mental insight mechanism and consequently
lead to the systematic examination of this aspect of design creativity.