Physics

...blessed and happy. It is called "all at once" to distinguish it from time, which is not all at once, but rather one part has passed and another part is in the future. And it does not use "at once" to imply a simultaneity of parts original: "simultate partium", but rather "at once" meaning there is no distance or interval. It is called "perfect" to distinguish it from that which is not entirely simple, just as that which it measures is not simple; for "perfect" is used here in place of "simple."

And note that eternity is spoken of analogically original: "anologice"; meaning the word is used in related but different ways—that is, in a primary and secondary sense—regarding both the Creator and his creatures. For there are three conditions of eternity properly so-called: namely, that it is simple, invariable, and interminable original: "iterminabile"; meaning boundless or without limit. In this context, "interminable" refers not only to a lack of an end, but also to a lack of a beginning; in this sense, it belongs to the Creator alone. For He truly is the only one who is simple, invariable, and without beginning or end.

However, certain creatures participate in the name of "interminability" in their own way. For example, angels and blessed souls, and even bodies after the resurrection, participate in the name of interminability because they lack an end, though they did have a beginning. Because of this, angels, blessed souls, and resurrected bodies are said to be eternal and to exist in eternity. They are called "eternal" because of their lack of an end; they are said to be "in eternity" because of their lack of change or invariability.

Furthermore, some creatures participate in eternity by reason of interminability because they lack an end—such as the punishments original: "pene"; referring to the eternal suffering of the damned which are called eternal—but they are not said to be "in eternity" because they do not participate in the state of invariability. For "invariability" or "unchangeableness" denotes a state of well-being. But this condition of simplicity is found "simply" in no creature.

Additionally, eternity signifies a superior measure regarding both its beginning and its end. Thus, some creatures, such as those that are generated and subject to decay, are excluded from eternity; they are neither eternal nor do they exist in eternity.

Therefore, some things are eternal and in eternity in the proper sense [God]. Some are not so in the proper sense: of these, some are eternal and in eternity through participation Angels and souls, who share in God's changelessness; some are eternal through participation but not "in eternity" [the damned]; and some are neither eternal nor in eternity but are excluded from eternity altogether. A fourth category cannot exist: namely, that something could be "in eternity" through participation but not be "eternal." For everything that is unchangeable lacks an end, but the reverse is not necessarily true.

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Next follows the "now" of eternity, of which Boethius says in his book On the Trinity that "the now that stands still and does not move itself makes eternity." This is better understood by making a comparison to the "now" of time.

Let us imagine a line, a to c, and let b be a point moving on that line from a to c, distinguishing what is before from what is after. We call the first part "passed," and the latter part "to be passed." Similarly, understand the line a-c to represent all of time, and understand b to be the now of time itself, which moves continuously from a to c. That which has been passed, we call the "past"; that which is to be passed, we call the "future." And just as on a physical line the moving point b always subtracts from the space ahead and adds to the space behind...