In mathematics, a constraint is a mathematical statement (loosely speaking, an equation) that is added to a model to help pin down a solution. That is, there can be an infinite number of potential solutions, but the addition of a constraint pins it down to a single solution. The grand-daddy of financial constraints -- the inter-temporal governmental budget constraint -- meets this technical definition.
Otherwise, we have non-mathematical definitions, e.g., the inflation constraint, as described by Modern Monetary Theory (MMT). Although constraint in this context is less clearly defined, I would argue that a key property is that it is always binding, and must hold.
The received wisdom among Canadian elites at present is that although it would be a mistake to tighten the Federal fiscal stance now, tightening should be done later (e.g., these comments). (This folk wisdom is probably showing up in other developed countries, but not as repetitively.) These elites might not refer to a "financial constraint" on the Federal government, but it is clear that they are not worried now about the alleged negative effects of issuance. That is, if a financial constraint did exist, it can be ignored in recessions, but it pops back into existence later. It is clear that this does not meet any reasonable definition of "constraint," it is a non-biding guideline of some sort.
This is unlike a household or a sovereign that borrows in a foreign currency, that always has to keep in mind the restrictions placed on it by creditors. (Yes, a floating currency sovereign has to meet existing debt obligations-- which might be viewed as a constraint -- but we are interested in the ability to add new debt.)
In summary, if we accept the premise that the government can wait for after a recession to worry about its finances, then we can say that it does not face a financial constraint. Given that the former appears to be a consensus view, the non-existence of financial constraints is not particularly radical.
Completely Obscure Technical Appendix on the Inflation Constraint
If one is unhappy with the mathematical status of the "inflation constraint," we can operationalise it mathematically as follows.
Property (name to be determined): An economic model has the (as-yet unnamed) property if at any time, a sufficiently large "loosening" shock to fiscal policy (G-T sufficiently negative) results in the price level (spot or forward) rising above some threshold relative to the model solution in the absence of the shock.
That is, loosen fiscal policy enough, prices go up.
All we need to is:
- Demonstrate that models we like have this property.
- Demonstrate that models that do not have this property display pathological behaviour.
This is a model property, and might not meet the usual mathematical definition of a constraint. (Although it is a constraint on the class of models considered.) However, it is a limitation on fiscal policy that holds at all times, so it meets my criticism about "non-binding guidelines."
(c) Brian Romanchuk 2020