Mental workload estimation has been under extensive investigation over the years, because the capability of monitoring the cognitive workload enables the prevention of cognitive overloading and improvement of workplace safety. Electroencephalogram (EEG) signals has been found to be an objective and non-intrusive measure of mental workload. However, the evaluation of cognitive workload based on single-trial EEG data, which is an essential step towards real-time workload monitoring and brain-computer interface, has been a major challenge. The philosophical basis is the similarity of technical images, the probability of dependence on image shape is similar; the ethical basis is that the experimenter's voluntary former is the external foundation; the latter two constitute the intrinsic foundation. It distinguishes the objects and concepts in the whole philosophical tradition In particular, it poses a challenge to the proposition of phenomenology that there is a fundamental distinction between the matter's intention and the concept's intention, so it has to face the problem of the philosophy of science of phenomenology.