This comes from Sextus Empiricus, the Pyrrhonian skeptic, speaking out against conceptions of time. This comes from Against the Physicists II.
“Let this, then, serve as our account of the difficulties regarding the real existence of time which arise from the conception of it; but we can also establish our case by means of direct argument. For if time exists it is either limited or unlimited; but neither is it limited, as we shall establish, nor is it unlimited, as we shall show; therefore time is nothing.
For if time is limited, there was once a time when time did not exist, and there will one day be a time when time will not exist. But it is absurd to say either that there was once a time when time did not exist, or that there will one day be a time when time will not exist, for the statements that “there once was” and that “there will be” are (as I said before) indicative of different times. So, then, time is not limited.
-Nor, in fact, is it unlimited. For one part of it is past, the other future. Each of these times, then, either exists or does not exist. And if it does not exist, time is at once limited, and if it is limited the original difficulty remains- that there was once a time when time did not exist and there will one day be a time when time will not exist. But if each exists- I mean both past and future time,- each will be in the present. And as existing in the present, both past and future time will be in present time. But it is absurd to say that past and future are conceived as in present time. So, then, time is not unlimited either.
But if it is neither conceived as limited nor as unlimited, it will not exist at all. – Also, what is composed of non-existents will be non-existent- of the past which exists no longer and of the future which does not as yet exist; time, therefore, is non-existent.
Furthermore: if time is anything, it is either indivisible or divisible; but it cannot be either indivisible, as we shall show, or divisible, as we shall establish; no time, therefore, exists.
Now time cannot be indivisible, since it is divided into past, present, and future. And it will not divisible because everything divisible is measured by a part of itself; the cubit, for instance, is measured by the palm, and the palms, is a part of the cubit, and the palm is measured by the finger, and the finger is a part of the palm. So, then, if time too is divisible, it ought to be measured by some part of itself.
But it is not possible for the other times to be measured by the present. For if the present time measures the past, the present time will be in the past, and being in the past it will no longer be present but past. And if the present measures the future, being within this it will be future and not present.
Hence, too, it is not possible to measure the present by the other times; for, as being within it, each of them will be present and not either past or future. But if one must certainly conceive time as either divisible or indivisible, and we have shown that it is neither divisible nor indivisible, it must be declared that time is nothing.
Furthermore: time is tripartite; for one part of it is past, one present, and one future. And of these the past no longer exists and the future does not yet exist. It remains to say that one part exists, the present.
The present time, then is either indivisible or divisible. But it cannot be indivisible, for “nothing divisible is of a nature to exist in indivisible time,” as Timon says, – becoming, for example, and perishing, and everything of a similar kind. And if it is indivisible, it will neither have a beginning whereby it is joined on to the past, nor an end whereby it is joined on to the future; for that which has a beginning and an end is not indivisible. But if it has neither a beginning nor an end, it will not have a middle either; for the middle is conceived by way of comparison in its relation to the other two. And as having neither beginning nor middle nor end, it will not exist at all.
And if present time is divisible, it is divided either into existent times or into non-existent. And if it should be divided into non-existent times, it will no longer be time; for that which is divided into non-existent times will not be time. And if it is divided into existent times, it will no longer, as a whole, be present but one part of it will be past, another future. And for this reason it will no longer, as a whole, be [present and] existent, as part of it no longer exists and part of is not as yet existing. But if of the three times- past, future, and present- it has been proved that not one exists, no time will exist.
And those who assert that present time is the limit of the past and the beginning of the future,- thus making one out of two non-existent times,- making not only one but every time nonexistent.
– And further : if present time is the limit of past, and the limit of the past has passed away together with that whereof it is the limit, present time will no longer exist, if it really is the limit of the past.
– And again; if present time is the beginning of the future, and the beginning of the future does not yet exist, present time will not yet exist, and thus it will have most opposite properties; for inasmuch as it is present it will exist, but inasmuch as it has passed away together with the past it will exist no longer, and inasmuch as it accompanies the future it will not as yet exist.
But it is absurd to conceive the same time as both existing and not existing, and no longer existing and not yet existing. So, then, in this way too one must deny that any time exists.
One may also argue thus: if time is anything, it is either imperishable and ingenerable or perishable and generable; but it is neither imperishable and ingenerable, as shall be proved, nor perishable and generable, as this also shall be established; time, therefore, is not anything.
Now it is not imperishable and ingenerable, seeing that part of it is past, part present, and past future. For the day of yesterday exists no longer, that of to-day exists, and that of to-morrow has not yet come into existence. Hence one part of time (namely, the past) no longer exists antoher (namely, the future) does not yet exist. And for this reason time will be neither ingenerable nor imperishable.
– But if it is perishable and generable, it is hard to say what it will perish into and from what it will come to exist. For neither does the future exist already, nor the past exist any longer. But how can a thing (come into existence) from non-existents, (or how can a thing) perish (into non-existents)? Time, then, is nothing.
One may attack it also in this way; if time is anything, it is either generable or ingenerable, or partly generable and partly ingenerable. But time cannot be either generable or ingenerable or partly generable and partly ingenerable; therefore time is not anything.
For if it i were generable, since everything which is generated becomes in time, time too being generated will be generated in time. Either, then, it will be generated as itself in itself or as one time in another.
And if it is generated as itself in itself, it will be a thing which has come to exist before it has come to exist; which is absurd. For since that in which a thing becomes must exist before that which is generated in it, time also, as generated in itself, must have come into existence before itself; just as a statue is wrought in a workshop, but the workshop existed before the statue, and a ship is constructed in a certain place, but the place was existing before the ship, So, then, if time too becomes in itself, it will exist before itself; and thus, inasmuch as it becomes, it will not yet exist, since everything which becomes, while it is becoming, does not exist as yet; but inasmuch as it becomes in itself, it must exist beforehand. Time, then, will be at once both existent and non-existent. Inasmuch as it becomes it will not exist, but inasmuch as it becomes in itself it will exist. But it is absurd that the same thing at the same instant should both exist and not exist; therefore it is also absurd to say that time becomes in itself.
-Nor yet does it become as one time in another,- the future, for instance, in the present, and and the present in the past. For if one time becomes in another, each of the times will necessarily quit its own position and occupy the post of the other. If, for example, the future time becomes in the present time, the future as becoming during the present will be present and not future; and if the present becomes in the past, as becoming during the past it will certainly not be present but past. And the same argument applies if we reverse their order, making the past becoming in the present and the present in the future; for her again the same difficulties follow.
– if, then, time does not become either in itself or as one time in another, time is not generable itself or as one time in another, time is not generable. But if it is neither ingenerable nor generable, and besides these one can conceive no third possibility, one must declare that time is nothing.
Now the fact that it cannot be ingeneralbe is extremely easy to demonstrate. For if it is ingenerable and neither has become nor will become, one time alone, the present, will exist, and neither will the future, and the things therein, be any longer future, nor will the past, and the things done therein, be any longer past. But this is not so; nor, consequently, is time ingenerable.
Nor yet is it partly generable and partly ingenerable, since, if so, the difficulties will be combined. For the generable must become either in itself or in another; but if it becomes in itself it will exist before itself, and if in another it will no longer be that time but , quitting its own post, it will be the time during which it becomes. And the same argument applies also to the ingenerable; for if it is ingenerable, neither will the future time every exist nor the past, but one time only remains, then, to say that as time is neither generable nor ingenerable, nor partly generable and partly ingenerable, time does not exist.”