A semantic field of oppression permeates the poem with blake choosing a restricted lexis:"charted","mind forged manacles" and "mark".He describes the "Thames", naturally free flowing, to have become "chartered", connoting restriction. He is scathing of the sheer control the authorities have, it even seeping down into nature- the oppression is so powerful that even nature is not exempt from its detrimental impact. - This links back to tropes of Romantic poetry, centralising their poetry around nature. Blake inverts this and makes it current with the bleak setting he is in, reinforcing how the awe-inspiring sublimity of nature is being tainted through political corruption.