'A university student is never seen to be writing or reading during the day time but she always submits her assignments in time. Therefore one can conclude that she must be studying and writing during the night time.' According to Mimamsa School of Classical Indian Philosophy, which instrument of knowledge (pramana) is used in the above argument?

Two facts sit in apparent conflict: she is never seen studying by day, yet she always submits her work on time.

The only way to reconcile them is to suppose she studies and writes at night.

This kind of postulation, made to explain an otherwise unaccountable fact, is presumption.

The unseen night study is assumed precisely because without it the timely submission stays unexplained.

In the Mimamsa scheme this means of knowledge is arthapatti.

So the pramana used here is arthapatti, presumption.