What it Means to be a Master

How would you define a master? Denise Levertov, the American poet, offers one definition by comparing a master to a Mountain:

Not one who one imitates, emulates even, but rather, a powerful presence acknowledged, looked up to in all weathers, A mountain. A great upheaval of rock and earth. Contours, declivities, the tufted ridge that defines the horizon, curly bloom of foggy woods, a rock…