If you affirm the reality of a fact past or present, your affirmation is of necessity determinately true, or it is determinately false, _i.e._ the contradictory negation is determinately true. But if you affirm the reality of a fact to come, then your affirmation is not by necessity determinately true, nor is the contradictory negation determinately true. Neither the one nor the other separately is true: nothing is true except the disjunctive antithesis as a whole, including both. If you say, To-morrow there will either be a sea-fight, or there will not be a sea-fight, this disjunctive or indeterminate proposition, taken as a whole, will be true. Yet neither of its constituent parts will be determinately true; neither the proposition, To-morrow there will be a sea-fight, nor the proposition, To-morrow there will not be a sea-fight. But if you speak with regard to past or present--if you say, Yesterday either there was a sea-fight or there was not a sea-fight--then not only will the disjunctive as a whole be true, but also one or other of its parts will be determinately true.[20] [Footnote 20: Ibid. p. 18, b. 29. Ammonius (Scholia ad De Interpret. p. 119, bb. 18, 28, seq.) expresses Aristotle's meaning in terms more distinct than Aristotle himself: [Greek: mê\ pa/ntôs e)/chein to\ e(/teron mo/rion tê=s a)ntipha/seôs _a)phôrisme/nôs a)lêtheu=on_], &c. (b. 43).] This remarkable logical distinction is founded on Aristotle's ontological or physical doctrines respecting the sequence and conjunction of events. He held (as we shall see more fully in the Physica and other treatises) that sequences throughout the Kosmos were to a certain extent regular, to a certain extent irregular. The exterior sphere of the Kosmos (the _Aplan=es_) with the countless number of fixed stars fastened into it, was a type of regularity and uniformity; eternal and ever moving in the same circular orbit, by necessity of its own nature, and without any potentiality of doing otherwise. But the earth and the elemental bodies, organized and unorganized, below the lunar sphere and in the interior of the Kosmos, were of inferior perfection and of very different nature. They were indeed in part governed and pervaded by the movement and influence of the celestial substance within which they were comprehended, and from which they borrowed their Form or constituent essence; but they held this Form implicated with Matter, _i.e._ the principle of potentiality, change, irregularity, generation, and destruction, &c. There are thus in these sublunary bodies both constant tendencies and variable tendencies. The _constant_ Aristotle calls 'Nature;' which always aspires to Good, or to perpetual renovation of Forms as perfect as may be, though impeded in this work by adverse influences, and therefore never producing any thing but individuals comparatively defective and sure to perish. The _variable_ he calls 'Spontaneity' and 'Chance,' forming an