IC maintains that Nothing is Absolutely True. The Shorter Oxford gives several meanings for ‘absolute,’ all deriving from the root meaning of detached or disengaged; in religion, for example, absolution detaches from sin. The most explicit of these is the one numbered IV.3: ‘Existing without relation to any other being; self-existent’ and (in the attached quotation): ‘that which exists in and by itself having no necessary relation to any other being.’ IC uses ‘absolute’ in this sense, to mean that which has no relation to anything outside itself. Truth being a quality of propositions, an absolutely true proposition would be one which included the whole truth within itself, excluding none (since exclusion is a relation).
This quality of detachment, of being unaffected by anything outside, gives the everyday sense of the term, as in: ‘I absolutely agree,’ or: ‘Oh yes, absolutely.’ Such remarks are intended to convey that the statement being approved contains the whole truth, leaving no more to be said. Similarly with various technical meanings, as when the political scientist describes Louis XIV as an absolute monarch and the physicist calls the speed of light an absolute. Here ‘absolute’ indicates that Louis enjoyed power unlimited by any parliament or constitution and that light always comes past you at the same speed, whether you travel towards the source or away from it. In these connections, however, the freedom from external influences falls short of completeness; the powers of all rulers are subject to limitation, if only by the need to preserve a body of subjects that they may continue to rule, and if the speed of light were not related to the points passed it could not be measured; it is invariant rather than, in the full sense, absolute.
Evidently a proposition true only under certain circumstances is related to those circumstances and therefore not absolute. Also, a proposition related to any other proposition is not absolute. Every proposition that asserts anything (positive or negative) excludes the contrary, and exclusion is a relation. It follows that in order to be absolute, unrelated to anything outside itself, a proposition must include its contrary, must deny what it asserts. In doing this it cancels the assertion, reduces it to nothing. The only absolute propositions are those that assert nothing.
It is not only self-cancelling propositions which amount to nothing but also those which assert nothing in the first place. These also are absolutely true. Unfortunately (or fortunately, if you enjoy logical puzzles) it is not always self-evident that a given proposition is asserting nothing; frequently examination is needed to reveal that a statement which seems to be conveying information is in fact not doing so. Margaret Chisman has been thinking about this, and has come up with some examples of statements which seem to assert something and also to be absolutely true (thus disproving NIAT) but which turn out on analysis to amount to nothing.
Each of my ancestors must have had at least one child. Anybody who becomes an ancestor must have had at least one child; when the statement is fully explicated it turns out to be saying that each of these people who must have had at least one child must have had at least one child. This conveys no information, it provides an instance of the nothing that IC asserts to be absolutely true.
We have all been children. This is not even completely true in an everyday sense. In the absence of specification that ‘all’ has to mean all human beings, and some of these are (not ‘have been’) children. In order to be completely true the proposition needs amending: All adults have been children. That makes it absolutely true since an adult is one who has been a child. But it now says only that all those who have been children have been children, and this tells us absolutely nothing.
We will all die. This is doubtless a reasonable expectation, but we cannot demonstrate its truth in advance. (Some Christians expecting the Second Coming would deny it). If we were to say All the dead have died, that would be absolutely true since the dead are those who have died. But it says only that those who have died have died and this, again, tells us absolutely nothing.
In response to an earlier issue of IC Bob Black asks whether it is not absolutely true that nothing is absolutely true. Indeed it is, but this is a confirmation of NIAT, not a refutation of it.
NIAT links up with systematic ideology, for if it be accepted that no proposition is absolutely true, that the contrary always contains some part of the truth, it follows that no major ideology can be absolutely valid; the others also have something to contribute. ((IC is not alone in this perception. It has been said, for example, of Isaiah Berlin: ‘His entire philosophical experience could be examined as a theoretical battle against the belief that in principle there is a truth which is the one and only valid answer to the central problems of mankind through history.’) 
Are we then to abandon the pursuit of truth? Just the contrary. It is the mistaken belief that absolute truth has been attained, ‘I am (absolutely) right, you are (absolutely) wrong,’ that puts a stop to the search. The recognition that we shall never reach absolute truth opens the way for a never-ending, ever-closer, approximation to it.
 Ramin Jahanbegloo 1992 Conversations with Isaiah Berlin. Peter Halbann
from Ideological Commentary 56, May 1992.