Learn English – Plural or Singular After a List of Items

grammatical-number

Given the sentence:

The password must be at least 8 characters long, contain at least one lower-case and one upper-case case letter(s) and a digit.

Should the word "letter(s)" be in singular or plural? Why?

EDIT: To avoid discussion on the password policies, please consider another example:

Today I've seen one yellow, one blue and one green bird(s).

Best Answer

To avoid sounding awkward and perhaps being ambiguous, I would recommend rephrasing your requirement.

The password must be at least 8 characters long and contain: at least one lowercase letter, at least one uppercase letter, and at least one digit.

To add my own input, this sort of password requirement will also tend to require at least one symbol and it should also list the acceptable symbols.