The work a songwriter brings into a co-write and the work the session produces together are different things legally — but without a record made before the session begins, only the second kind of evidence ever exists.
A Nashville songwriter walks into a co-write Tuesday morning with three half-finished ideas she has been working on for months. One is a verse melody and lyric she has been refining since a long drive in February. Another is a chord progression and topline she demoed alone in her studio in March. The third is a song title and hook idea she has been carrying around since last autumn.
The session goes well. By Friday a finished demo exists. Two months later, the song is cut by a major-label artist. Six months after that, it is the lead single from a number-one album. The cue sheet is filed with three co-writer credits, each receiving a third of the songwriter share.
She knows the verse melody was hers. She knows the chord progression underneath the chorus was hers. She knows the title was hers. Her co-writers remember the room differently. Her publisher accepts the cue sheet as filed.
Nobody is acting in bad faith. There is no objective record of who brought what. Three months of work she did before the session became, by the equal-split convention, a one-third share on a song paying tens of thousands a year. The co-write problem is not usually about dishonesty. It is about the absence of anything except memory — and memory is not evidence.
Before the legal analysis: the numbers. PRS for Music distributed £1.02 billion in royalties to songwriters, composers and publishers in 2024 — the first year the total has cleared the billion-pound mark. In streaming, songwriters and publishers collectively receive approximately 20 per cent of platform revenues, with the remaining 80 per cent allocated to performers and labels. On a major-label number-one, a songwriter's share of the composition can run to tens of thousands of pounds annually across performance, mechanical, and synchronisation income. When the split is one third of that rather than two thirds — because the pre-existing contributions that went into the room cannot be evidenced — the financial difference is not trivial. It compounds over the song's term, which runs for 70 years from the death of the last surviving joint author.
When splits are contested, the commercial damage arrives before any lawsuit. A performing rights organisation — PRS for Music, ASCAP, BMI, or any other — that receives conflicting registration data from co-writers will freeze all royalties on the disputed works until the conflict is resolved. The money sits in what the industry calls black-box income. Resolving the dispute requires all co-writers to reach agreement or proceed to a formal process. During that period, which can run to months or years, nobody collects.
The starting point under UK law is section 10 of the 1988 Act, which defines a work of joint authorship as one made by two or more authors where the contribution of each is not distinct from that of the others. That definition contains a trap for co-writers who do not document their pre-session material. If contributions are distinct — independently separable — they belong to separate authors. If they are not distinct, the result is joint authorship, with all the equal-ownership consequences that carries.
Pre-existing material introduced into a session is, in principle, distinct: it was made before the collaboration, it has an independent existence, and the songwriter who made it should be the sole author of that element. But that argument depends on proving the pre-existing material existed and was brought into that session. Without a record predating the session, there is no way to distinguish a chord progression written in March from a chord progression suggested by someone else in the room on Tuesday.
US copyright law asks the same question through a different frame. Under the Ninth Circuit's test in Aalmuhammed v Lee (2000), joint authorship requires each contributor to have intended, at the time of creation, that their contribution be part of a joint work — not merely that they contributed something. A songwriter who brings pre-existing material into a session and can prove it pre-dates the session is in a stronger position to resist a joint-authorship claim over those elements: the intent at the time of the pre-session creation was not to co-author with anyone. Two English cases show both sides of what happens when the question is litigated. In Hadley v Kemp [1999], Gary Kemp was found to be the sole author of the Spandau Ballet songs, despite the other band members performing on the recordings. The court found that what the other members contributed was to the sound recording — the performance — rather than to the underlying musical composition. In Fisher v Brooker [2009], the House of Lords reached the opposite conclusion: the Hammond organ introduction to A Whiter Shade of Pale, created by Matthew Fisher in the weeks leading into the recording sessions, was a sufficiently original contribution to the musical work to earn a joint authorship credit, despite a thirty-eight-year gap before the claim. The case illustrates both that pre-existing contributions can earn authorship credit and that relying on recollection to establish them — across four decades of denial — is a long and expensive road. The evidence of the original contribution existed, barely, in the recollections and early recordings that survived. Most sessions leave far less.
In a co-write dispute, the question of who contributed what is almost never resolved by reference to objective evidence, because objective evidence rarely exists. Each songwriter believes their own recollection of the room. There is no neutral party. Audio recordings of the session are typically absent, and where they exist, they usually begin once the song has started taking shape — after the moment when pre-existing material was introduced.
Voice memos on the original songwriter's phone might exist, dated to months before the session. Whether they carry any weight depends on the phone's metadata, which can be altered, and on whether some independent source corroborates that memory. Email threads might show a rough idea shared before the session — but only if such an email exists, and only if it identifiably contains the specific element later in dispute.
What usually remains is the split sheet: the formal document filed with performing rights organisations. Once filed and accepted, challenging it requires evidence the songwriter rarely holds. The equal-split convention is not unfair in every case — within a small, repeating community of writers, the imbalances of one session tend to correct in the next. It becomes unfair at the extremes: when one writer brings substantially more pre-existing material than others, or when the resulting song generates the kind of royalties where every fraction of a percentage point matters.
The professional co-write market has expanded well beyond the small repeating communities where the equal-split convention first developed. According to an October 2025 analysis by Downtown Music (downtownmusic.com), co-written singles accounted for 63 per cent of UK chart entries by 2020, up from 44 per cent in 2015, and roughly half of all number-one hits in the United States and the UK are now co-written. That growth reflects the expansion of the songwriting camp model, where publishers and labels bring groups of writers to a single location for several days, with each session pairing two to four writers and a producer. These intensive sessions can pair writers who have never met and will not meet again; the output of a successful week can number a dozen songs, each with its own attribution question. In that environment, the relationship assumptions the convention relied on no longer hold.
Pre-session prior proof does not mean documenting every idea or lyric in advance. It means creating a verifiable record of the specific material being brought into a particular session, before the session takes place. A voice memo of the verse melody, recorded in February. A MIDI export of the chord progression, drafted in March. A typed lyric draft of the hook line, written last autumn. Each is a digital file. Each can be deposited in a private vault before the songwriter walks into the room Tuesday morning.
What the deposit produces is a cryptographic fingerprint tied to that exact file, a timestamp confirming when the deposit was made, and a blockchain anchor that makes the record permanent. The contents of the files remain private — only the songwriter can access the originals. What becomes available, if needed, is the fact that those specific files existed in those specific forms before the session.
If a dispute later arises, the songwriter can produce the original files, demonstrate that their hashes match the certificates in the vault, and establish — to a court, to a publisher, or to a performing rights organisation — that the verse melody, the chord progression, and the hook line all pre-dated the co-write by months. The split sheet may still need to be re-negotiated. The publishing agreement may still need to be revisited. But the conversation begins from evidence, not from competing memory.
Cryptographic prior proof at the qualified standard works in four layers:
The deposit process takes under a minute and works from the same files a songwriter produces anyway: the voice memo on the phone, the MIDI export from the DAW, the lyric draft in the notes app. Nothing about the creative process changes. What changes is whether the process leaves a record.
A vault deposit made before a session never needs to be mentioned in the room. It exists quietly in the background, available only if it is ever needed. The songwriter walks in knowing that, regardless of how the room remembers things in three years, her contributions are documented. That assurance changes almost nothing about the session itself and everything about the position she is in if the session ever becomes a dispute.
The broader discipline makes the position stronger still. A songwriter who deposits material before each session builds, over time, a continuously dated portfolio of pre-existing work. Each piece is independently verifiable. Walking into any co-write with that record behind her, she is not relying on memory or goodwill. She is relying on evidence. That shift in position is quiet, invisible to the room, and permanent.
For the session itself, the practical step is simple. Treat the vault deposit as one more part of the preparation — alongside the voice memo backing up to the cloud, the email to the publisher updating on the idea, the note added to the project file. The preparation that protects the work demands less effort than the preparation that leaves no record.
Why the song splits conversation is one you can't afford to avoid — PRS for Music M Magazine
Fisher v Brooker [2009] UKHL 41 — BAILII
How to Prove You Created Something: A Practical Guide for Anyone Who Makes Original Work
This post provides general information about the role of cryptographic evidence. It is not legal advice. For advice on a specific matter, consult a qualified lawyer in your jurisdiction.
James Snell is the founder of Provlyn, a platform providing cryptographic prior proof of IP ownership. provlyn.com