When a poet wishes to utter thoughts that are too unformulated, that lie too deep, for words—
Break, break, break,
On thy cold grey stones, O Sea!
And I would that my tongue could utter
The thoughts that arise in me—
he has recourse to simile and metaphor. Take, for example, the transience of human life, a subject on which at times we most of us have keen vague thoughts that, we imagine, would be so profound could our tongues but utter them.
Blake's Thel is a symbol of the transience of life.
O life of this our Spring! why fades the lotus of the water?
Why fade these children of the Spring, born but to smile and fall?
"Thel, the transient maiden, is.... What is Thel?" says Blake, in effect. Thel cannot be described straightforwardly. "What then is Thel like?"