Strict determinism and strict arbitrarism are not, however, the sole adversaries of the concept of liberty-necessity, as rigorous materialism and mysticism are not the only adversaries of idealism. There exists another which must be called more dangerous (if misunderstanding be more dangerous than error). This doctrine, since it goes by the name of dualism, spiritualism, and neocriticism in general philosophy, could be called the doctrine _of double practical causality,_ in the field of the practical problem. The supporters of this line of thought, despite many individual differences, are all agreed in positing two distinct series of facts: one which obeys mechanical causality, another which is initiative and creation, or (as they say) obeys causality through freedom. There are thus two series that interpenetrate one another or alternate at every instant and are mutually blended, the one in the other. Hence there is something of each in the volitional act, something of the strongest motive and something of free choice. Such a solution has some external resemblance with that which we maintain, but is intrinsically most different. Our solution is _fusion_ of liberty and necessity, while this is _juxtaposition;_ our solution is _conciliation,_ this _transaction._ Like every juxtaposition and transaction it displeases both the contending parties, and falls into the power, now of the one, now of the other. Thus, if, according to the theories of that tendency, it be maintained that freedom exists, but that there are also causes tending to diminish it, or that there exist volitional acts, but that involuntary acts also exist, one does not understand how a series of facts that has its own law in itself (freedom, the will) can ever be subordinated to facts that obey a different law (diminution of freedom, involuntariness of acts). If this happen sometimes or many times, we must suspect that it happens always, and that the surviving freedom is a mask of freedom, illusion. Thus, if it be affirmed that side by side with causality, with equivalence of causes and effects, or with the possibility of foreseeing the effect by means of the cause, there is another causality, in which the effect is not equivalent to the cause, and that not only is it not to be foreseen, but is such that only after it has happened does it allow its cause to be discovered; then the doubt arises that one of the two causalities does not exist, because either the effect is equivalent to the cause, and so it must always be, or it is not equivalent to it, and so it will never be; or it can be foreseen by means of the cause, and so it will always be, or it cannot be foreseen, and never will be foreseen. The strict determinists and arbitrarists have the loyalty of error, and they are rare, because energetic spirits are rare, but the doctrine of double causality is tinged with some of the rouge of truth, and thus seduces the many,