सुप्रभातम् - चरकसंहिता - सूत्रस्थानम् - दशमोऽध्यायः

सुखसाध्यं मतं साध्यं कृच्छ्रसाध्यमथापि च।

द्विविधं चाप्यसाध्यं स्याद्याप्यं यच्चानुपक्रमम् ॥

साध्यानां त्रिविधश्चाल्पमध्यमोत्कृष्टतां प्रति।

विकल्पो न त्वसाध्यानां नियतानां विकल्पना॥

(चरकसंहिता-सूत्रस्थानम्-१०/९-१०)

Curable diseases are of two types- one that can be cured easily and the other with some difficulty. Similarly, incurable diseases are of two types, viz., one which is palliable and the other which is absolutely irreversible. Again, the curable diseases have three alternants depending upon the moderate and excellent methods required to cure them. This alternative is, however, not possible with regard to diseases which are absolutely incurable.

(Charakasamhita Sutrasthanam 10/9-10)