The dead cannot object. This is the central ethical fact of writing about them, and it is the problem that makes the act of writing about a dead friend different from all other personal writing. The memoirist who writes about a living person risks a confrontation, a lawsuit, the end of a relationship; the one who writes about a dead friend risks something harder to name: the betrayal of a person who trusted you with themselves and is no longer present to correct your account.
The literary tradition of elegy and memoir is substantially a tradition of writing about dead friends. Montaigne's essays were written in the shadow of La Boétie's death; the essays are, among other things, a decades-long reckoning with what it means to continue existing after the person who knew you most completely has stopped. Tennyson's In Memoriam is one hundred and thirty-three cantos of grief for Arthur Hallam. Walt Whitman's elegy for Lincoln is also an elegy for the young men he cared for during the Civil War. Samuel Johnson's lives of poets are inflected throughout by the deaths of people he knew. The impulse to write about the dead friend is not an eccentric private response to loss; it is one of the most persistent drives in the literary tradition, the form through which culture processes the fact that individuals die while the language that describes them persists.
But writing about a dead friend is also an act of power over someone who cannot respond. Every decision the writer makes — which moments to include, which character traits to emphasize, how to characterize the friendship, what private things to reveal — is made unilaterally. The dead friend becomes a character in someone else's narrative, subject to the same distortions and omissions that any character suffers, with no recourse. The writer who loves the dead friend may distort them through idealization; the writer who had a complicated relationship with the dead friend may distort them through the unresolved entanglement of grief and resentment. Neither distortion is dishonest in intent; both are distortions.
At the collective level, the aggregate of writing about dead friends constitutes a significant portion of what culture knows about how people actually lived. Biography, memoir, elegy, the obituary written by someone who actually knew the deceased — these are the forms through which private life becomes historical record. The person who writes about a dead friend is doing, without necessarily knowing it, an act of social documentation: making visible a relationship that would otherwise leave no trace. The quality of that documentation — its honesty, its complexity, its willingness to present a full person rather than a flattened saint — matters for the social record.
The permission question is never fully resolvable. A person cannot obtain posthumous consent. What they can do is ask, before the death if it is foreseeable, what the person would have wanted written or not written; construct a picture of what the person would have wanted based on their expressed values and their demonstrated preferences around privacy; and write with a level of care and specificity that reflects actual knowledge of the person rather than the projection of one's own grief onto a shape that used to be them. This last is the hardest: to write about a dead friend without making the essay secretly about yourself.