Indefinite Adjectives and Pronouns
Related to the interrogative adjectives and pronouns is another group of words called indefinite adjectives and pronouns. They are similar in form to the interrogatives, and like the interrogatives they stand in for unknown or unexpressed persons or things. The most common words of this class are:
quī dam, quaedam, quoddam (someone, something, a certain)
quisque, quidque (each)
quisquis, quidquid (whoever, whatever; quisquis is almost always seen in the nominative)
aliquis, aliquid (anyone, anything)
In form, the words quī dam and quisque are simply quī and quis with the suffixes -dam and -que. In the cases where the forms of quī and quis end with the letter m (i.e., accusative singular and the genitive plural), the m changes to an n. For example, if you add -dam to que m the result is que ndam.
There is an old rhyme that says “After sī -, nisi, num, and nē all the ali-'s fall away.” This means that when aliquis follows any of the words in that little list, you will see only forms of quis (e.g., sī -quis advē nit, “if anyone came”).