All extremes of feeling are allied with madness.

The line suggests that when emotions become absolute—whether joy, grief, love, anger, or fear—they can tip into a state where judgment and proportion fail. “Allied with madness” does not necessarily mean clinical insanity so much as a kinship between emotional extremity and mental disorientation: the mind becomes unmoored, perception distorts, and ordinary social or rational constraints loosen. Read in a Woolfian key, it also reflects a modernist suspicion of grand, totalizing states (of feeling or thought) and a preference for nuance, gradation, and the shifting textures of consciousness. The aphoristic form implies a hard-won observation rather than a moralistic warning.