There's a hallowed, oft-booted, but never released Pink Floyd single that would've been the band's last moment with founding guitarist and main man Syd Barrett called "Scream Thy Last Scream." You can hear how such an eviction was inevitable (maybe even necessary) for that imminent classic-rock behemoth to blow up like inflatable pigs when it did: Syd sounds deranged, demented, singing of strangling that "old woman with a casket." And yet, that boyish side of him glimmers at the same time: In a sped-up pixie voice, he also chimes splendid gibberish like "flack-chap-chau-fauses-mouses-houses." Whimsical and frightening, its four minutes encapsulate his well-publicized madness, careening between extremes of violence and wonderment. Hell, the song even anticipates his lodging in his Mum's basement with the windows boarded up to keep out fans and journalists alike, boasting about "watching the telly 'til all hours."

And that's what Syd's renowned legend became, an Icarus soaring high on daily doses of LSD who mentally melted and flamed out from the next decade's biggest album artist. Instead of world tours and playing at Pompeii, he was on the couch, packing on the pounds. It's the "crazy diamond" cautionary tale that not only shines on, but obfuscates and overshadows the once-brilliant artist: the dark, long-tressed frontman, the sonic alchemist, the clever songster, the laughing madcap, the disintegrating balladeer, and the savage, destabilized guitarist. Sure, he died July 7 from diabetes (in front of the telly, no doubt), but he had left earth for permanent interstellar overdrive some three decades previous, his quirky promise barely realized.

"You can't hear me, but I can you," Barrett keens on Pink Floyd's 1967 debut (and to some fans, the only Pink Floyd album), The Piper at the Gates of Dawn, grinning like a Cheshire cat mid disappearing act. Initially known in hip galleries and avant-garde performance spaces as a rock band offering open-ended, head-expanding, largely improvised music, Barrett and crew tempered such sprawl in the studio. Drawing on his own hallucinatory visions, Lewis Carroll, The Wind in the Willows, as well as the I Ching, Syd instead cut bright, head-swimming singles. Pink Floyd's earliest sides, "See Emily Play" and "Arnold Layne," charmed with both doe-eyed and perverse characters on display.

Yet instability and chaos beckoned at every chord change. Barrett's childlike voice would clench up and bare fangs by the chorus; cuckoo clocks, shortwave radios, kazoos, or Salvation Army marching bands could break through at any moment, abandoning the rational song altogether. Such outbursts subverted yet electrified their pop, and up until he psychically fell apart by 1968, it seemed that almost any surreal sound, image, or string of words could suddenly fit inside a pop song; it's an idea taken up by everyone from Radiohead and Robyn Hitchcock to the Flaming Lips and Animal Collective in the subsequent decades.

Be it on Floyd's bridges and interludes or else on longer instrumentals like "Pow R. Toc H." and "Interstellar Overdrive," such instances already reveal an anxious inner space latent in Syd. He savagely attacks chords (his jags anticipate Gang of Four and Fugazi) only to stagger off-task immediately: His tone fraught and unsettling one second, it coheres and suggests new noises and vistas the next.

As he ventured further afield in his head, playing with the more-sober bandmates in Pink Floyd began to bore him. Legend tells of a late-era Syd song with ever-changing chords and words, never the same song twice, something that perhaps only Heraclitus would dig. That mischievous, clever wink, so evident on Piper, turns glazed for large portions of his two solo albums from the 1970, The Madcap Laughs and Barrett. Half-assembled ideas, ramshackle takes, and song sketches act like the Roman ruins do, their broken and crumbling forms merely intimate and mark a once-glorious epoch, even if Syd's only lasted from 1965 to 1967.

And yet when that ingenuous effulgence burns through, on songs like "Octopus," "Gigolo Aunt," and "Terrapin" (or when he sneakily tapes his backing band just warming up), it's as if Syd never really disappeared from terra firma. Even in a mental freefall, his lyrics suggest a lucidity about his own deteriorating state: "Jugband Blues," his lone contribution to Pink Floyd's A Saucerful of Secrets, openly jokes about his disappearing act, musing aloud, "I'm wondering who could be writing this song."

Whether physically dead or living dead, Syd makes us instead wonder what it would've been like for him to have been at the helm when the band aimed for the Dark Side of the Moon, or for concept albums capricious rather than portentous. Who knows what a once-beautiful mind like his could've ultimately conjured?