Why Bonds And Equities Are Combined At All

The conventional portfolio combines shares and bonds, and the reasoning is often reduced to a slogan about balance. The actual mechanism is more specific and has identifiable limits.

The two claims sit at different points

A bond is a contractual obligation to pay defined amounts on defined dates. A share is a residual claim on whatever remains after those obligations are met.

That difference in seniority means the same business conditions affect each differently. Bondholders are unaffected by a company doing better than expected, while shareholders receive the surplus.

The result is that bonds have a narrower range of outcomes and shares a wider one, before considering anything about interest rates or inflation.

They respond to different variables

Government bond prices are driven largely by interest rate expectations and the perceived safety of the issuer. Share prices respond to expected profits and the rate used to discount them.

When growth expectations weaken, profits are marked down while rate expectations often fall too, which supports bond prices at the same time.

This is the mechanism behind the traditional pairing. It is a relationship between how each asset reacts to conditions rather than a rule that one rises when the other falls.

The relationship is not constant

When inflation is the dominant concern, both assets can fall together, because higher rate expectations reduce bond prices while also lowering the value placed on future profits.

The correlation between the two has varied considerably across different economic periods, and the helpful pattern is a feature of particular conditions rather than a permanent property.

Portfolios built on the assumption that bonds always offset equity falls are therefore relying on something that holds most of the time rather than always.

Bonds do more than one job

They provide income, they provide something to sell when equities have fallen, and they reduce the overall variation of the portfolio. These are related but distinct functions.

Which function matters most depends on the holder's situation, particularly whether money is being added to the portfolio or drawn from it.

Short-dated and long-dated bonds serve these purposes very differently, which is why the split between them is a separate decision from the overall bond weighting.

Credit quality changes the character

Bonds issued by companies with weaker finances behave more like equities under stress, because the concern in both cases is whether the business can meet its obligations.

Adding such bonds to increase yield therefore reduces the diversifying effect that the bond portion was included to provide.

Distinguishing between the safety component and the yield component of a bond allocation clarifies what each part is actually there to do.