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We can't subsist on hope alone.
The noun forms of the verb to subsist are subsistence and the gerund, subsisting.
to be able to survive or stay alive
It means to consume, or to exist, to get by on. (e.g. I subsist on corn flakes.)
Note : "to be formed of" is consists (e.g. The Earth's core consists of two parts.)
Exist, reside, subsist, abide, dwell...