Ellicott's Commentary on the Whole Bible

Matt. 25:46: Everlasting punishment--life eternal. The two adjectives represent the same Greek word (aionion) aionios -- it must be admitted (1) that the Greek word which is rendered "eternal" does not, in itself, involve endlessness, but rather, duration, whether through an age or succession of ages, and that it is therefore applied in the N.T. to periods of time that have had both a beginning and an ending (Rom. 16:25), where the Greek is "from aeonian times;" our version giving "since the world began." (Comp. 2 Tim. 1:9; Tit. 1:3)--strictly speaking, therefore, the word, as such, apart from its association with any qualifying substantive, implies a vast undefined duration, rather than one in the full sense of the word "infinite."

The Encyclopedia Dictionary of the Bible (Catholic Bible Dictionary), p. 693

ETERNITY: The Bible hardly speaks of eternity in the philosophical sense of infinite duration without beginning or end. The Hebrew word olam, which is used alone (Ps. 61:8; etc.) or with various prepositions (Gn. 3:22; etc.) in contexts where it is traditionally translated as "forever," means in itself no more than "for an indefinitely long period." Thus, me olam does not mean "from eternity" but "of old" (Gn. 6:4, etc.). In the N.T. aion is used as the equivalent of olam.

Dr. F.W. Farrar, The Eternal Hope, p. 198

That the adjective is applied to some things which are "endless" does not, of course, for one moment prove that the word itself meant "endless," and to introduce this rendering into many passages would be utterly impossible and absurd.

Dr. F.W. Farrar, Mercy and Judgment, p. 378

Since aion meant "age," aionios means, properly, "belonging to an age," or "age-long," and anyone who asserts that it must mean "endless" defends a position which even Augustine practically abandoned twelve centuries ago. Even if aion always meant "eternity," which is not the case in classic or Hellenistic Greek-- aionios could still mean only "belonging to eternity" and not "lasting through it."

Hasting's Dictionary of the New Testament, Vol. 1, p. 542, art. Christ and the Gospels

There is no word either in the O.T. Hebrew or in the N.T. Greek to express the abstract idea of eternity.

(Vol. III, p. 369) Eternal, everlasting--nonetheless "eternal" is misleading, inasmuch as it has come into the English to connote the idea of "endlessly existing," and thus to be practically a synonym for "everlasting." But this is not an adequate rendering of aionios  which varies in meaning with the variations of the noun aion from which it comes.

The Interpreter's Dictionary of the Bible, Vol. IV, p. 643

Time: The O.T. and the N.T. are not acquainted with the conception of eternity as timelessness. The O.T. has not developed a special term for "eternity." The word aion originally meant "vital force," "life;" then "age," "lifetime." It is, however, also used generally of a (limited or unlimited long space of time. The use of the word aion is determined very much by the O.T. and the LXX. Aion means "long distant uninterrupted time" in the past (Luke 1:10), as well as in the future (John 4:14).

Lange's Commentary American Edition, Vol. V, p. 48

On Ecclesiastes 1:4. The preacher, in contending with the universalist, or restorationist, would commit an error, and, it may be, suffer a failure in his argument, should he lay the whole stress of it on the etymological or historical significance of the words, aion, aionios, and attempt to prove that, of themselves, they necessarily carry the meaning of endless duration.

Dr. MacKnight

I must be so candid as to acknowledge that the use of these terms, "forever," "eternal," "everlasting," shows that they who understand these words in a limited sense when applied to punishment put no forced interpretation upon them.

The Parkhurst Lexicon

Olam (aeon) seems to be used much more for an indefinite than for an infinite time.

G. Campbell Morgan, God's Methods With Men, pp. 185-186

Let me say to Bible students that we must be very careful how we use the word "eternity." We have fallen into great error in our constant usage of that word. There is no word in the whole Book of God corresponding with our "eternal," which as commonly used among us, means absolutely without end.

The New Schaff-Herzog Encyclopedia of Religious Knowledge, Vol. XII, p. 96

Under the instruction of those great teachers, many other theologians believed in universal salvation; and indeed the whole Eastern Church until after 500 A.D. was inclined to it. Doederlein says that "In proportion as any man was eminent in learning in Christian antiquity, the more did he cherish and defend the hope of the termination of future torments." Many more church historians could be quoted with similar observations.

Philippson, Israel Religionslehre (11:255)

The Rabbi teach no eternity of hell torments; even the greatest sinners were punished for generations.

Dr. Alford Plumer, An Exegetical Commentary on the Gospel of Matthew, pp. 351-352

It is often pointed out that "eternal" (aionios) in "eternal punishment" must have the same meaning as in "eternal life." No doubt, but that does not give us the right to say that "eternal" in both cases means "endless."

Dr. Edward Plumptre (Eschatologist)

I fail to find, as is used by the Greek Fathers, any instance in which the idea of time duration is unlimited.

The Pulpit Commentary, Vol. 15, p. 485

It is possible that "aeonian" may denote merely indefinite duration without the connotation of never ending.

G. T. Stevenson, Time and Eternity

(Page 63) Since, as we have seen, the noun aion refers to a period of time, it appears very improbable that the derived adjective aionios would indicate infinite duration, nor have we found any evidence in Greek writing to show that such a concept was expressed by this term.

(Page 72) In 1 Cor. 15:22-29 the inspired apostle to the Gentiles transports his readers' thoughts far into the future, beyond the furthest point envisaged elsewhere in holy writ. After outlining the triumph of the Son of God in bringing all creation under His benign control, Paul sets forth the consummation of the divine plan of the ages in four simple, yet infinitely profound words, "God all in all." This is our God, purposeful, wise, loving, and almighty, His Son our Lord a triumphant Savior, Who destroys His enemies by making them friends.

Jeremy Taylor, author of Systematic Hellology, which advocates the common belief in eternal torment, later writes a modified view in Jeremy Taylor's Works, Vol. III, p. 43.

Though the fire is everlasting, not all that enters it is everlasting . . . . "The word everlasting signifies only to the end of its period.

Dr. Nigel Turner, Christian Words, p. 457

All the way through, it is never feasible to understand aionios as everlasting. 

Dr. (Prof.) Marvin Vincent, Word Studies of the New Testament, Vol. IV

(Page 59) The adjective aionios in like manner carries the idea of time. Neither the noun nor the adjective in themselves carries the sense of "endless" or "everlasting." aionios means enduring through or pertaining to a period of time. Out of the 150 instances in the LXX (Septuagint), four-fifths imply limited duration.

(Page 291, about 2 Tim. 1:9) "Before the world began" (pro chronon aionion) Lit. Before eternal times. If it is insisted that aionion means everlasting, this statement is absurd. It is impossible that anything should take place before everlasting times.

Charles H. Welch, editor of The Berean Expositor, wrote in An Alphabetical Analysis, Vol. I

(Page 52) What we have to learn is that the Bible does not speak of eternity. It is not written to tell us of eternity. Such a consideration is entirely outside the scope of revelation.

(Page 279) Eternity is not a Biblical theme.

Dr. R.F. Weymouth, The New Testament in Modern Speech, p. 657

Eternal: Greek: "aeonion," i.e., "of the ages." Etymologically this adjective, like others similarly formed, does not signify "during," but "belonging to" the aeons or ages.