By Ted Hughes
The thought fox is a poem about writing a poem. The poet is sitting in a room late at night, it's dark outside and though he can't see anything he senses a presence:
Something else is alive
Beside the clocks loneliness
And this blank page where my fingers move
This presence is in the poet's imagination, as you find out in the very first line:
I imagine this midnight moments forest:
It immediately shows a contrast between the first two lines. The first line takes place in the real world', after the colon we enter the realm of the poet's imagination. The presence' is an idea stirring in the deep dark night of the poet's mind and it is represented by a fox. This fox is in the midnight forest inside the poet's head; therefore it is also in the study (I don't know it is a study, I just assume so) where the poet is writing this poem. It is already alive (as is the clock, with its ticking like a heartbeat), already present, but it has no form yet. The poet's mission is to gently coax it out of its shapelessness, and turn it into a poem.
The poet looks out of his window, a window which in this case has a double meaning. The second double colon and the fact that it is in the exact same position as the first one means that it is a window in the real world', a window in the poet's study through which tonight he sees no stars. The other meaning of the window is the window of his consciousness. He is looking inside to find the poem that is there, waiting to come out. Everything in the world inside his head is still dark due to the lack of stars. He doesn't know what it is that will emerge from the darkness.
Through the window I see no star:
Something more near
Though deeper within darkness
Is entering the loneliness:
The presence the poet has sensed is nearer than the stars, as it is right there in his own mind. Yet that makes it no clearer, only deeper within darkness as the stars shed no light on it. But...