Components of GDP: Stable or Unstable?

• Now we can say:

        GDP         ≡   C        + I     + G         + (X - M)

                        Stable     ???     Stable       Stable

• So if GDP is unstable, where is the source of its instability?

        GDP         ≡   C        + I     + G         + (X - M)

        Unstable        Stable     ???     Stable       Stable

• Only category left: Investment spending (I)