6 ideas
Hokusai's postscript dismisses everything he drew before seventy as unworthy of notice and dates the start of real understanding to seventy-three. The claim is that the first fifty years of practice build the capacity to see, and only after that does the work begin to register the true structure of its subject.
The postscript sets out a projected curve of development. At seventy-three he partly grasps the structure of animals, birds, insects, fish, and the growth of plants. At eighty he expects further progress, at ninety to penetrate the essence of things, at a hundred to reach the divine, and at a hundred and ten to make every dot and line alive. Each decade is assigned a specific competence, so ageing becomes a schedule of widening perception rather than decline.
The endpoint of mastery is defined at the smallest unit of the work: a single dot or stroke that carries life by itself. The standard moves the measure of skill from composition and subject down to the vitality of each individual mark.
The book returns to a single mountain again and again, placing it in the background of work, festivals, legends, weather, and reflections. It shows that a fixed object is never exhausted, because each change of vantage or context reveals a different Fuji. Repeatedly studying one subject is presented as a way of deepening perception, not as repetition.
Fuji often appears small or incidental: glimpsed through a cooper's barrel, behind roofers, or beyond workers and travellers in the foreground. Making the sacred mountain secondary to daily activity places the transcendent inside ordinary life rather than apart from it.
Hokusai links his wish to live very long directly to his artistic aims, treating a long lifespan as the necessary condition for reaching mastery. His pursuit of the immortal mountain echoes this hope to extend life, so the work itself becomes an argument for endurance and continued practice as the path to excellence.