Note 3 — Chapter VII

Footnote 3: The modification was that causation is not only "invariable" but also "unconditional" sequence. This addition of unconditionality as part of the meaning of cause, after defining cause as the sum total of the conditions, is very much like arguing in a circle. After all, the only point recognised in the theory as observable is the invariability of the sequence. But this is less important than the fact that in his canons of the Experimental Methods Mill recognised that more is observable.