Q:

R - aov() - only do two-way interactions

If I'm running an ANOVA in R using aov(), how do I limit the interaction terms to only two-way interactions? For example, this code: 
model <- aov(y ~ a * b * c, data=data)
summary(model)

will create a model with a, b, c, ab, ac, bc, and abc. How can I limit this so the only interactions that appear in the model are ab, ac, and bc? I've tried
aov(y ~ a .*. b .*. c, data = data)

but that threw an error.

A:

In a formula, the ^ operator limits interaction terms to the specified order:
aov(y ~ (a + b + c)^2, ...)

