ces._

To exclude a supposed Cause: (a) Any agent that can be introduced among
certain conditions without being followed by a given phenomenon (or that
is found without that phenomenon); or (b) that can be removed when that
phenomenon is present without impairing it (or that is absent when that
phenomenon is present), is not the cause, or does not complete the
cause, of that phenomenon in those circumstances.

To exclude a supposed Effect: (c) Any event that occurs without the
introduction (or presence) of a given phenomenon; or (d) that does not
occur when that phenomenon is introduced (or is present), is not the
effect of that phenomenon.

* * * * *

Subject to the conditions thus stated, the rules may be briefly put as
follows:

I. (a) That which (without further change) is followed by a given event
is its cause.

II. (a) That which is not so followed is not the cause.

I. (b) That which cannot be left out without impairing a phenomenon is a
condition of it.

II. (b) That which can be left out is not a condition of it.

B. QUANTITATIVE DETERMINATION

The Equality of Cause and Effect may be further explained by these
rules:

III. (a) When a cause (or effect) increases or decreases, so does its
effect (or cause).

III. (b) If two phenomena, having the other marks of cause and effect,
seem unequal, the less contains an unexplored factor.

III. (c) If an antecedent and consequent do not increase or decrease
correspondingly, they are not cause and effect, so far as they vary.

It will next be shown that these propositions are variously combined in
Mill's five Canons of Induction: Agreement, the Joint Method,
Difference, Variations, Residues. The first three are sometimes called
Qualitative Methods, and the two last Quantitative; and although this
grouping is not quite accurate, seeing that Difference is often used
quantitatively, yet it draws attention to an important distinction
between a mere description of conditions and determination by exact
measurement.

To avoid certain misunderstandings, some slight alterations have been
made in the wording of the Canons. It may seem questionable whether the
Canons add anything to the above propositions: I think they do. They are
not discussed in the ensuing chapter merely out of reverence for Mill,
or regard for a nascent tradition; but because, as describing the
character of observations and experiments that justify us in draw