“We had to lock the doors to make [Blue],” Joni Mitchell is quoted saying in Sheila Weller’s Girls Like Us. “Nobody was allowed in. If you looked at me, I would weep.” Though Mitchell has, throughout her career, assiduously and vehemently rejected the use of the term “confessional” to describe her songwriting, these naked, seemingly autobiographical odes to love and disillusionment have been inspiring over-sharers with pianos ever since. The buoyant and soulful “Carey” was written about Cary Raditz, a stern and adamantine cave-dweller who romanced Mitchell during her time spent slumming with a hippie cult in the Greek village of Matala; the song is, along with “My Old Man,” one of the few on Blue to heedlessly celebrate a love affair despite its imperfections. But Raditz was not the only inspiration discovered on Mitchell’s European adventures, nor was he the only one that would become immortalized on Blue: somewhere along the way Mitchell purchased an Appalachian dulcimer, a lithe, meek sounding instrument that would foreground many of the album’s songs. On “River,” Mitchell bemoans a California Christmas, and a “crazy scene” from which she desperately wants to retreat. The performance is masterful; you can almost see the frost misting over the piano keys, emitting icy vapor with each hammered strike. The roving “A Case Of You” was reportedly written about Leonard Cohen, and its amphibological title is merely the tip of an ambiguous iceberg: When Mitchell likens the subject to liquid — “I could drink a case of you/ and still be on my feet” — is it a come-on or an insult? Blue is full of such magnificent moments; it is the rare album that, like a philosophical epiphany or some pivotal life event, contains the power to change the way you experience the living world. It is no coincidence it remains Mitchell’s most beloved, revered and enduring album.