Seeing "se" in "Ram wrote with a pen" (Ram ne kalam se likha), Mohan thinks "se" always shows…

Why

Mohan has locked 'से' to one job, based on sentences like 'पेड़ से पत्ता गिरा' (a leaf fell FROM a tree), where 'से' does show separation. But the same word 'से' can do different jobs in different sentences, depending on the relationship between what comes before and after it. In 'राम ने कलम से लिखा', 'कलम' (pen) isn't something Ram separated from — it's the INSTRUMENT that made the writing possible; here 'से' shows means or instrument, not separation. Test it: 'चाकू से काटा' and 'कैंची से काटा' — in both, 'से' names the tool used, with no separation involved. His teacher is right: here 'से' shows the instrument (करण कारक, karan karak) — what the action was done WITH — not every 'से' means the same thing.