That which is especially auxiliary in the accomplishment of the action is called Instrument or karaṇa kāraka,
A दात्रेण लुनाति he cuts with the sickle. परशुना छिनत्ति he divides by the axe. The instrument कारक takes the third-case affix.
Why do we say 'especially'? Because in the case of the other karakas, the non-mention of the word 'especially' makes it possible for us to use those cases, in not their strict sense. Thus though the locative case should be used where strictly a thing is located in another, yet we may say गङ्गायां घोषः the herdsman in the Ganges, not strictly in, but on the banks of, the Ganges. कूपे गर्गकुलम् the family of frogs in the well, i.e. on the sides of the well.,