Improper structures arising from the estimation of parameters in structural equation models (SEMs) are commonly an indication that the model is incorrectly specified. The use of boundary solutions cannot in general be recommended. Partly on the basis of theory given by Van Driel, and partly by example, suggestions are made for using the data as evidence of the type of misspecification and as a guide to the appropriate model. Three types of improper structure suggested by Van Driel are reviewed, and a 4th type is introduced.