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67. If- a cause is necessary to the existence of an effect, th 

 effect cannot exist without it; if the effect depends upon the 

 cause, and cannot exist without it, then there must be some virtue 

 in the cause, by which the effect is produced. So far, so good: 

 we next come to this virtue in a cause. 



68. A cause is a form of existence. A form of existence has 

 no virtue to be either more or less than itself; the most then that 

 a cause can do, is to exist. Thus, an acid can be neither more nor 

 less than an acid; or if it ceases to be an acid, it is because this 

 form of existence unites with another, as, recurring to our example, 

 with an alkali; and conjointly they produce another form of exis- 

 tence, which other form of existence is the effect; and the causes 

 are necessary to the existence of the effect, because the effect it 

 the existence of the causes, and the existence of the causes is that 

 of the effect. The reason why a cause appears to produce some- 

 thing different from itself, is that in the effect there is a double 

 relation of existences with our faculties of perception; that is, an 

 effect is made by the union of differential forms of existence. 

 These forms of existence in their separate state have a separate 

 relation with our faculties of perception : in their united state, the 

 relation of two forms of existence with our faculties is comprised 

 in one ; and hence an effect appears one form of existence, different 

 only from its causes, because the causes when separate have an 

 individual relation with our faculties, and when united they have 

 only one or an aggregate relation with our faculties of perception. 

 The perception of this one undivided relation of causes, comprised 

 in an effect, is frequently superseded in matters of experimental 

 philosophy .by inference. Thus atmospherical air appears one form 

 of existence; but our inferences teach us, while contemplating a 

 sphere of vision without sensible objects, that the atmosphere 

 which occupies this range consists of oxygen and azote ; and if 

 our means of analysis were more perfect, we should ascertain it 

 to consist of fifty thousand things besides. From the same quar- 

 ter may be drawn many similar examples, which, as they are 

 similar, it is unnecessary to mention. 



69. Succession is admitted to prove causation; but we dis- 

 tinguish between succession which does, and which does not im- 

 ply dependence. When one form of existence regularly succeeds 

 to another, and regularly ceases when that other is removed, thqn 

 we experience that the existence of one is dependent upon that of 

 the other;. and that the effect will succeed to the causes, and will 

 not exist when these are absent, in all future instances, is an in- 

 ference founded upon universal past experience. This is the suc- 

 cession which proves the relation of cause and effect; and the 

 .proof is established upon these, analytical and synthetical tests. 



70. But when an antecedent is occasionally only followed by 

 a certain consequence; or, more .satisfactorily, when the conse- 

 quence may .exist without the antecedent ; then this succession 

 does not prove causation, uor .cau it be admitted, as a proof. But 



