In the poem "London," what kind of langauge is the phrase, "mind-forged manacles" (e.g., literal, figurative, image, what is the image)?
The lines you ask about in Blake's "London" follow:
In every cry of every Man,
In every Infant's cry of fear,
In every voice, in every ban [public pronouncement, announcement of marriage],
The mind-forg'd manacles I hear.
"Mind-forg'd manacles" is figurative language--metaphorical, to be more specific. The human tendency to abandon his/her own liberty is compared to shackles or chains that imprison a person when he/she is captured. The handcuffs are of our own creation. The handcuffs are created within our own minds. Our own chains are forged or created in our own minds. We allow ourselves to give up our liberty.
The metaphor creates a figurative image for the reader. What that image exactly consists of may vary from reader to reader, however. In other words, what you picture or hear when you read about manacles being forged within a person's mind might be different from what I picture or hear. But whatever auditory and visual images it precisely creates, it draws together the cries and voices and pronouncements of the stanza, and combines them to reveal our self-created, or at least, allowed, loss of liberty.
The cries, etc., for the speaker, demonstrate the "mind-forg'd manacles."