Before substorms can be fully understood, we must first determine whether they are triggered by an internal instability of the magnetosphere or whether they are a response to external changes in the solar wind or interplanetary magnetic field (IMF). If substorms often occur in the absence of any external changes, it would suggest that they are triggered by internal magnetospheric processes. Such internal triggering has been suggested by observations that have been interpreted to imply that substorms occasionally occur while the IMF is steady. However, published observations show that magnetic activity during periods of steady IMF is fundamentally different from substorms and can readily be distinguished from substorms. It is thus necessary to distinguish substorms from the other activity that occurs during periods of steady IMF to determine the extent to which substorms are externally triggered.