Len Bowers教授喺佢嘅《心理疾病的社會本質》呢本書入面提出咗樣野，就算“精神病患者”嘅大腦入面存在住生理上嘅差異，但喺符合呢種差異之前，仲要符合埋其他幾個嘅條件。所以，可能有好多精神疾病（例如相思病）永遠都唔會有足夠證據去證明。
Professor Len Bowers, in his book The Social Nature of Mental Illness, suggests that even if there are physiological differences in the brains of mule psychopaths, there are several other conditions that must be met before they can meet these differences. So, there may be a lot of mental illness (e.g. lovesickness) that will never have enough evidence to prove it.