The main objective of this study is to analyze the reasoning of university students regarding two laws of electromagnetism: Gauss's law (in electric field) and Ampere's law (in magnetic field). It has been supposed that the problems observed in the understanding and application of both laws do not only come from students's misconceptions. Students habitually use reasoning based on 'common sense' methodology that leads to a form of reasoning, known in the literature as 'functional reduction' and 'functional fixation'. To test our hypothesis five open problematic situation, with an emphasis on explanations, were designed. The results obtained seem to confirm that university students have serious difficulties in understanding and applying both of the above mentioned laws
