Substitutes and Complements¶

Why It Matters¶

Whether goods are substitutes or complements determines how demand responds, how pricing strategies work, and how markets interact. If your product is a complement to something popular, ride the wave. If it's a substitute, you're competing directly.

The Key Move¶

For any two activities or goods, ask: does more of one increase or decrease the value of the other? If doing A makes B less valuable, they're substitutes. If doing A makes B more valuable, they're complements. This determines strategic implications.

Classic Application¶

Platform strategy. iOS apps are complements to iPhones. More good apps make iPhones more valuable. Apple's strategy rationally subsidizes app development (through developer tools, App Store promotion) because apps are complements to its hardware.

Surprising Application¶

Work and leisure skills. Many leisure activities are substitutes for work (you do one or the other). But some are complements - exercise that increases energy, reading that builds skills, relationships that provide support. Structuring leisure as complementary to work rather than substituting for it changes its value.

Failure Modes¶

• Treating all alternatives as substitutes - some alternatives are actually complements at the system level
• Ignoring that substitute/complement relationships can change - goods that were substitutes can become complements with new technology
• Missing indirect relationships - goods can be complements to something that's a substitute to your product
• Treating the relationship as symmetric - A might be a stronger substitute for B than B is for A
• Ignoring network effects that can turn substitutes into winner-take-all competition

Go Deeper¶

Standard microeconomics texts cover this. Platform economics literature (Rochet and Tirole) develops the strategic implications.