Why does the author say that 'the tension must be conveyed and must be sustained'?

Explanation

Tension arising from contradiction is part of the poem's meaning, so it must be carried through. Options 1 and 2 describe logical connectives, not tension.

Note: Passage II (from William Empson, Seven Types of Ambiguity, 1930) is copyrighted and is not reproduced. Its argument: logical connectives are often unnecessary or misleading; the 'forces' that hold a poem's ideas together are mostly carried inside the ideas, so ideas are easier to name than forces; forces and ambiguity are complementary, so forces cannot be discussed simply as ambiguity; where a poem holds a contradiction, the tension must be conveyed and sustained.