It is tempting to say that a retirement plan should preserve purchasing power, and then move on to the interesting questions about allocation and fees.
I could not move on, because the phrase conceals at least half a dozen different targets, and the choice among them changes every judgment that comes after it.
Preservation might mean maintaining command over a consumer basket. That is the CPI meaning, and if it is the right one, then indexed government bonds largely solve the problem for anyone who can hold enough of them. It might mean replacement income, which is the actuarial meaning. It might mean access to housing, whose price travels independently of consumer baskets and has done so for two decades in most of the markets our employees actually live in. It might mean relative economic position, which no architecture can promise, because relative position is zero-sum by construction. It might mean financial independence, meaning a stock large enough that work becomes optional. Or it might mean command over future human production in the broadest sense, of which all the others are projections.
These are not the same target wearing different clothes. A system can satisfy one while failing another. A worker whose savings track the consumer basket perfectly can still watch the house recede. A worker with a textbook replacement ratio can still have no buffer for the shocks that arrive at 41 rather than 71.
Purchasing power is a family of claims. An architecture has to be told which member of the family it serves, and almost none of them are told.
The Proposal
The target is none of the assets and none of the indices. The target is the worker's own future liability.
A working life generates, on its far side, a stream of obligations: shelter, food, care, participation in ordinary life, sustained for a lifespan not known in advance, priced at prices not yet set. That stream is a liability in the actuarial sense. Personal rather than corporate, implicit rather than contractual, but a liability all the same. Preservation succeeds when accumulated capital can meet that liability as it falls due, and fails when it cannot, whatever the account statements said along the way.
Here is the sentence the rest of the paper leans on:
Preservation is not a property of assets. It is a relationship between assets and a future life.
That definition is less novel than it may sound, which is a strength rather than a weakness. It is how defined benefit pensions actually worked. The plan named a liability, and the entire actuarial and investment apparatus was organized against it. It is how liability-driven institutional investing works today, and has for decades. And it is the position Robert Merton has pressed for the defined contribution world: plans managed toward wealth are managed toward the wrong variable, because the worker's true objective is income, and wealth is only an intermediate with a treacherous exchange rate into income.
Neither liability matching nor retirement income adequacy is discovered here. What is new is the placement. Liability logic is applied downstream, where consequences are managed. I am proposing to apply it upstream, inside compensation architecture, where the increments are designed in the first place.
And if the liability is the target, then the liability, not any market convention, is the benchmark against which an employer's preservation architecture should be designed and judged. Different workers present different liabilities. Which is why I keep refusing to name a best asset. Assets cannot be best in the abstract. They can only be well or poorly matched to a liability.
Two Things That Follow Immediately
The popular proxies get demoted without being discarded. CPI-tracking becomes an administrative convenience standing in for the consumption portion of the liability. The replacement ratio becomes a summary statistic of liability coverage rather than the objective itself. And wealth becomes what it always was: an intermediate, useful, and not the thing being bought.
The second consequence matters more, because it disarms the objection everyone reaches for first. Yes, a thirty-year liability cannot be known exactly. It can be estimated in bands and updated as the life unfolds, which is what salary scales and actuarial valuations did for decades without anyone calling it impossible. The impossibility of perfect knowledge is an argument for adaptive architecture. It is not an argument for the current practice, which is to name no target at all.
That asymmetry is worth sitting with. We do not refuse to build salary structures because we cannot know what the market will pay in 2031. We build a structure, band it, and revise it annually. Nobody thinks this is fraudulent precision. Applied to preservation, the same discipline is treated as unreasonable, and the alternative that gets chosen instead is silence.
The Liability Has Tranches
One refinement makes the liability operational rather than merely conceptual, and it comes straight out of actuarial practice.
The future liability is not homogeneous. It has tranches.
A floor tranche: the non-negotiable minimum of shelter, food and care. It tolerates almost no shortfall.
A flexible tranche: the maintenance of an accustomed standard of living. It tolerates moderate shortfall.
An aspirational tranche: travel, bequest, the discretionary life. It tolerates substantial shortfall.
The design implications follow directly. The floor warrants the least risk and the strongest claim on pooling and guarantee. The aspirational tranche can afford risk the others cannot. I should be careful here: these are design propositions generated by the framework rather than empirically demonstrated conclusions. They are the tranche logic that every liability-driven institution already applies, transposed to the individual, and they await evidence.
What the tranches establish conceptually is enough for now. Different portions of the liability demand different architectures, which is why "which asset is best" is a malformed question before any of the harder analysis even starts.
And once you have the concept, a large amount of what we call preservation failure can be restated as tranche mismatch. Floor obligations funded at aspirational risk. Or the reverse, which gets far less attention and costs real money: decades of growth forgone to over-insure something that was never at risk.
The refinement has one fortunate property. Households already think this way. The behavioral literature documents that people naturally partition wealth into mental accounts with different purposes and risk tolerances. Tranche-structured architecture works with the grain of documented behavior rather than against it, which is not something you can say about most of what plan communication asks people to do.
One caution keeps it honest. The tranches are decision scaffolding, not valuation cells. They are elicited from a person whose preferences will move, and they should be revised on an annual cadence the way salary scales always were. A leaky partition that names the floor still beats the current practice, which names nothing.
The Practical Version
If you administer a plan, there is a question in here that costs nothing to ask and that almost no plan can answer: what is this plan's implicit liability posture?
Not the target-date glide path, which is a proxy for a proxy. The actual question. For this workforce, at this wage level, in these housing markets, what does the far side of a career cost, roughly, in bands? And does anything in the plan's design reference that number?
I have asked versions of this in enough conversations to know the usual answer, which is that the question has not previously come up. That is not a criticism of the people administering plans. It is a description of a gap in the discipline that trains them, and it is the gap this paper exists to describe.
Next week: once the target is a liability rather than an index, the most familiar number in finance stops meaning what we thought it meant.