Nina made two lists in the sand:

Things I can see, hear or touch	The know-how you learn
🥁 drum, 🎤 singer	🎵 music
👯 dancer, 👣 ghungroo	💃 dance
📓 notebook, 📏 ruler	➗ maths
🖼️ a drawing on the wall	✏️ drawing (the skill)
📜 a poem	✍️ poetry
🧲 magnet, 🌱 plant	🔬 science

"The left side can walk through the Sense Gate," said Nina. "I can hear a drum and touch a notebook. But the right side is the know-how inside people. Nobody can point at maths!"

"Wait!" said Nina. "Drawing is on BOTH sides!"

"Sharp eyes," said Grandpa. "When you say I am learning drawing or She is good at drawing, you mean the skill — the know-how in your hand and head. That is abstract. But when you say I made a drawing of Biscuit, you mean the picture on paper. You can pin it on the wall, point at it, even have two drawings. That is concrete."

"So if I can put a, the or two in front, and point at it on paper, it's a thing," said Nina. "Every day I practise drawing, and every day I get a new drawing for the wall!"

"So here is a little test," said Grandpa. "Try saying: I am learning ___. Or: I go to ___ class."

I am learning music. ✅ — a skill.
I go to dance class. ✅ — a skill.
I am learning maths. ✅ — a subject.
I am learning drum. ❌ — you learn to play the drum. The drum is a thing!

Nina frowned. "But you said if a sense can find it, it's concrete!"

"And that still works for every thing," said Grandpa. "Bell, drum, flute, thunder, air — all concrete. The guards find things. Music (the art) isn't a thing; it's the art of putting sounds together — the know-how that makes a tune, the way cooking makes a cake. You can taste the cake. You can't taste cooking!"

Nina giggled. "So I hear a drum, but I learn music."

"Hoo-hoo! That is right: the names of arts and subjects — like music and grammar — are abstract nouns. Invisible nouns. You'll meet more of them soon."

"But Kabir says music is concrete," said Nina, "because you can hear it!"

"Some people do say that," said Grandpa. "Grammar is not written in stone, and clever people sometimes sort words differently. Different grammar books sort it differently. We will say: music is an art, so it is abstract."

The Monster sighed and carried music away to join the invisible nouns, humming a tune. The tune, of course, was something everyone could hear.