Word Choice – Diagnosis or Diagnoses

BizWritingTip reader: “Would you please help me with the difference between ‘diagnoses’ and ‘diagnosis’? Are these words singular and plural?”

BizWritingTip response: “Diagnosis” is a singular word meaning the identification of an illness or disease by means of a patient’s symptoms.


Dr. House’s diagnosis was accurate – as usual.

The word “diagnoses” is the plural form.


It took several diagnoses before his residents reached the right conclusion.

“Diagnose” can also be used as a verb, meaning to distinguish or to indentify by diagnosis.


Dr. House will diagnose the problem correctly by the end of the show.