Page "Emil Kraepelin" Paragraph 17

One of the cardinal principles of his method was the recognition that any given symptom may appear in virtually any one of these disorders ; e. g., there is almost no single symptom occurring in dementia praecox which cannot sometimes be found in manic-depression.

What distinguishes each disease symptomatically ( as opposed to the underlying pathology ) is not any particular ( pathognomonic ) symptom or symptoms, but a specific pattern of symptoms.

In the absence of a direct physiological or genetic test or marker for each disease, it is only possible to distinguish them by their specific pattern of symptoms.

Thus, Kraepelin's system is a method for pattern recognition, not grouping by common symptoms.