Besoli, Stefano. 1984. "Convergences and Diversities between Noneism and Gegenstandstheorie." Grazer Philosophische
Studien no. 21:133-153.
"The problems that give rise to the conceptual system developed by Routley(1) are largely those suggested by the proposals contained in
Meinong's Gegenstandstheorie . By taking up these themes again Routley wishes to legitimate an ideal resumption, a radicalization and an expansion of
a number of theses peculiar to Meinongian doctrine. Starting from this remark, he is then led to deal explicitly with the limits of the internal presupposition
of classical logic, putting forward, by contrast, the advantages of a recomprehension which attempts to bring to light the logical/ontological topics generally
neglected or, rat her, reductionalistically interpreted within the framework of a Russellian theory of logic. The author's constant appeal to a neutral
ontology which is close, but not identical, to Meinong's range of Außersein permeates his entire work and supports the emergence of an idoneous theory
of items. The Leitfaden is the refutation of Standard Reference Theory (RT) which is the paradigmatic core common empiricism, idealism and
materialism, but which also underlies extensionally quantified orthodox logic.
Reference Theory (RT) requires, as an essential condition, that truth and meaning are rigid functions of reference. The original aim of
Routley's analysis is to eliminate the prejudice in favour of immediate actuality which is inherent in every referential view. Accordingly, it must be possible
to make semantically relevant the occurrence of non-referential statements.
Meinong's philosophical work, together with the influential theories of Th. Reid, suggests the inescapable clauses for a gnosiological
alternative which will not relapse into platonism." (p. 133)
(1) We refer mainly to Routley's Exploring Meinong's Jungle , Canberra, 1980, where he gives an enlarged draft of conceptual trends
established long ago.
Brady, Ross T. 1980. "Two Remarks on The Logic of Significance and Context ." Notre Dame Journal of Formal Logic
"I wish to make two remarks on two points that Goddard and Routley made in Chapter 5 of their book, The Logic of Significance and
The first remark is that the Brady disjunction, 'V',(1) does have applications in ordinary discourse, in answer to the doubts about this
expressed by them on pp. 344-5 of . I will defend this position, which I originally made in  on p. 30, and also in , pp. 172-3, by showing that each
of four examples can be interpreted in a way which requires 'V to be used in its formalization. The second remark is that the need for a functionally complete
significance logic such as their system S5 (or S6) seems very limited. I show this by examining each of their five
arguments for a functionally complete system on pp. 348-351 of  and by showing how their weaker significance-complete (for definition, see , p. 326)
system S3 (or S4) will suffice, except in exceptional circumstances, to express what they suppose a functionally complete
system is needed for." (p. 263)
(1) The symbols and terminology for this paper are taken from Goddard and Routley .
 Brady, R. T., "A 4-valued theory of classes and individuals," Ph.D. thesis, 1971, deposited in the University Library, St.
 Brady, R. T., "Significance logics," Notre Dame Journal of Formal Logic , vol. XVII (1976), pp. 161-183.
 Goddard, L. and R. Routley, The Logic of Significance and Context, Vol. 1, Scottish Academic Press, Edinburgh, 1973.
Bradley, Michael. 1978. "On the alleged need for nonsense." Australasian Journal of Philosophy no. 56:203-218.
"The theory, stemming from Russell, that there are grammatical sentences of English, containing only recognised English vocabulary,
which are nevertheless meaningless is a familiar landmark of contemporary Philosophy.
In recent years, however, the case for the non-significant has been taken up again. In a series of closely argued papers Ross Brady, Leonard
Goddard and Richard Routley have urged the necessity for nonsense, and the latter two authors have developed (in ) a logic of significance whose
justification is largely the supposed need for nonsense. In this paper I examine their reasons for alleging the need, and conclude that they have not
established a case.
Because of the extent of the collaboration and agreement between the authors cited it as often pointless to refer a view to one rather than
another. In such cases I use the phrase 'our authors'. In other cases where more accuracy seems called for, one or two of them are referred to by name.
Our authors call 'falsidal' those theories which treat sentences such as 'Virtue is square' and 'I likes dancing' as faIse (, p. 213;
, p. 368). They describe and criticise various versions of the falsidal approach, and find all of them deficient. What I wish to propose is a non-arbitrary
and epistemologically satisfactory falsidal theory which escapes the difficulties of other versions. I shall only try to assess the arguments given by our
authors so far as they seem or are claimed to bear on the falsidal theory which I am
going to propose. These arguments are scattered through a number of places and often conjoined with material not germane to the present task.
I have tried to abstract the strongest and clearest exposition of all ma (pp. 203-204)terial I think relevant. Not all the relevant writings by our three
authors are mentioned in my bibliography, but only those drawn on. Others will be found detailed in the bibliography to , and further relevant material in
the notes to  and ." (pp. 203-204)
1. Brady, Ross and Routley, Richard: 'Don't Care Was Made to Care', Australasian Journal of Philosophy 51 (1973) pp. 211-225.
3. Goddard, L. and Routley, Richard: The Logic of Significance and Context Volume I (1973).
10. Routley, Richard: 'On a Significance Theory', Australasian Journal of Philosophy 44 (1966) pp. 172-209.
11. Routley, Richard: 'The Need for Nonsense', Australasian Journal of Philosophy 47 (1969) pp. 367-383.
Hyde, Dominic. 2001. "Richard (Routley) Sylvan: Writings on Logic and Metaphysics." History and Philosophy of Logic no.
Abstract: "Richard Sylvan (né Routley) was one of Australasia's most prolific and systematic philosophers. Though known for his
innovative work in logic and metaphysics. the astonishing breadth of his philosophical endeavours included almost all reaches of philosophy. Taking the view
that very basic assumptions of mainstream philosophy were fundamentally mistaken, he sought radical change across a wide range of theories. However, his view
of the centrality of logic and recognition of the possibilities opened up by logical innovation in the fundamental areas of metaphysics resulted in his working
primarily in these two, closely connected fields. It is this work in logic and metaphysics that is the main focus of what follows."
Kielkopf, Charles. 1974. "Critique of the Routley's First Degree Semantics." Australasian Journal of Philosophy no.
"R. and V. Routley's 'The Semantics of First Degree Entailment '(1) is a clear, careful, but relatively non-technical presentation of a
semantics for Anderson and Belnap's so-called tautological entailments. Their paper is a valuable introduction to a treatment of negation in semantics for
relevant logics and entailment systems. However, the Routleys' paper is primarily an attempt to build a case for accepting as valid only the first degree
inferences warranted by the tautological entailments instead of the much larger class warranted by the tautologies of classical propositional logic. I adapt
terminology of the Routleys' to call the tautological entailments, and the first degree inferences warranted by them, FD logic. The Routleys'
semantics for FD logic is a special case of semantics for relevant logics(2) whose first degree fragment is the
tautological entailments. In my argument, I shall only sketch the basic idea of their semantics for FD logic since I shall not be
concerned with technical uses of the semantics for results Such as completeness. I shall argue that the Routleys' semantics for FD logic does not
justify switching from classical to FD logic. However, I shall recommend using their semantics for uncovering tautologies needed, in a special sense
of 'needed', in classically valid inferences." (p. 105)
"Indeed, I hope that I have shown that the Routleys, despite their intriguing semantics and illuminating discussion of suppression, have
given no good reasons for switching from classical to FD logic." (p. 120)
(1) Noûs 6 (1972) pp. 335-59. All references, unless otherwise specified are to this paper.
(2) See R. Routley and R. K. Meyer's 'The Semantics of Entailment, in H. Leblanc (ed.): Truth, Syntax and Modality , (1973) pp.
192-243; 'The Semantics of Entailment-lI,' Journal of Philosophical Logic (1972) pp. 53-73; 'The Semantics of Entailment-III,' ibid. pp. 192-203.
Section 5 of R. Routley's 'A Semantical Analysis of Implicational System I and of the First Degree of Entailment', Mathematische Annalen 196 (1972)
pp. 58-84, is especially helpful for showing that the set-up semantics to be considered here are semantics for the tautological entailments.
Lewis, David K. 1990. "Noneim or Allism?" Mind no. 99:23-31.
Reprinted in: D. Lewis, Papers in Metaphysics and Epistemology, Cambridge: Cambridge University Press, 1999, pp. 152-163.
"Some few entities - present, actual, particular, spatiotemporal, material, well-bounded things - exist uncontroversially. Scarcely any
philosopher denies them. Other alleged entities are controversial: some
say they exist, some say they do not. These controversial entities include past and future things, the dead who have ceased to be and those
who are not yet even conceived; unactualized possibilia; universals,
numbers, and classes; and Meinongian objects, incomplete or inconsistent or both. An expansive friend of the entities who says that all these
entities exist may be called an allist . A tough desert-dweller who
says that none of them exist may be called a noneist . In between come most of us, the pickers and choosers,
Richard Routley declares himself a noneist.(1)1 If we may take him at his word, he holds that none of the controversial entities exist. But
ay we take him at his word?" (p. 23)
"In short: we dispense with existence - but heed what this means and what it does not. Of course we do not dispense with the word
'exist' as one of our pronunciations for the quantifier. Neither do we dispense with a trivially universal predicate of existence, automatically satisfied by
absolutely everything. But if 'existence' is understood so that it can be a substantive thesis that only some of the things there are exist - or, for that
matter, so that it can be a substantive thesis that everying exists - we will have none of it." (p. 31, a note omitted)
(1) Richard Routley, Exploring Meinong's Jungle and Beyond: An Investigation of Noneism and the Theory ef Items (Australian National
University, 1980). For short: Jungle . Routley, as he then was, is now Richard Sylvan, but I shall refer to him by the name under which the book was
Meyer, Robert K. 1998. "In Memoriam: Richar (Routley) Sylvan 1935-1996)." The Bulletin of Symbolic Logic no.
"Besides free logic and his work on Meinong, Sylvan was an important contributor to the development of paraconsistent ideas, already in
the first degree semantical work with Val Plumwood cited above. This work led him into important collaborations with other logicians, as did his work on
relevant logics and on a number of other subjects. Besides those mentioned elsewhere in this note, among Sylvan’s important logical collaborators were Nicholas
Griffin, Graham Priest, Ayda Arruda, Dominic Hyde and Jean Norman.
Richard continually applied (and was continually turned down) for promotion to full Professor at ANU [Australian National University]. It is
probably not irrelevant that, in all his enterprises, he almost never chose the easy or popular course. His enthusiasms–logical, intellectual and
political–were for the alternative. To get the counter-suggestible Sylvan to defend some view, a good move was to remark that the view was now utterly
So Richard Sylvan is gone. It’s hard to believe; it would be in character for him to be fooling us, spreading the rumour of his death for
some deep Sylvanesque purpose. I personally miss him very, very much. When my own career was in ashes, it was Sylvan’s invitation to come Down Under in 1974
that brought it back to life. And now logic and philosophy have suffered a great, great loss. Greater than they know." (p. 340)
Paolini Paoletti, Michele. 2013. "Commentary: Exploring Meinong’s Jungle and Beyond: an Investigation of Noneism and the Theory of Items
by R. Routley." Humana.Mente Journal of Philosophical Studies no. 25:275-292.
"I cannot give here an exhaustive account of Routley’s whole investigation of noneism (i.e., the theory according to which, roughly,
there are items that do not exist, or, in other words, that not all the items exist). Considering the structure of the book, it is possible to individuate: a
brief presentation and defense of noneist theses (pp. 1–73); a critique of classical logic and the introduction of a revised, neutral (i.e., not existentially
committed) logic grounded on the theory of items (this long part includes, among other things, some important remarks on the Characterisation Postulate, on
identity, existence, possible worlds, inconsistency, definite descriptions, intensional contexts) (pp. 73–360); a defense of a Meinongian and presentist
metaphysical theory of time (pp. 361–409); some replies to Quine’s article On what there is (in the short paper On what there isn’t ) and to
other objections (pp. 411–488); the contiguity between noneism and common sense (pp. 519–536); noneist theories of fiction (pp. 537–606), of existence (pp.
697–768), of mathematical and theoretical knowledge (pp. 769–832) and of other topics (e.g., universals and perception) (pp. 607–696); Routley’s interpretation
of Meinong’s work (pp. 489–518) and the differences between Routley’s noneism and other theories of items (pp. 833–890); the paper Ultralogic as universal in
the Appendix (pp. 892–959).
In this brief commentary, I shall focus on Routley’s denial of the Ontological Assumption and on some theses, such as the Characterisation
Postulate and the distinction between characterising and non-characterising properties. Furthermore, I shall present and discuss Routley’s Meinongian
Presentism and his theory of fictional items." (pp. 275-276)
Parsons, Terence. 1983. "Review of Exploring Meinong's Jungle and Beyond. by Richard Routley." The Journal of Philosophy
"This book is an anthology of interconnected papers by the au- thor. Some have been previously published, but some, including the title
essay (Chapter 1, 259 pages), have not previously appeared in print. The theme of the book is a development and defense of a Meinongian theory of objects
(called "items" by Routley), coupled with attacks on the "empiricist, reductionist, anti-Meinongian" world view that is now a prevalent
theme in Anglo-American phil- osophy. Routley's views are in many ways closer to Meinong's than are those of any other current writer, and this alone would
make the work of interest. The book is highly programmatic; in this review I will not try to forecast the ultimate fate of the pro- gram, but instead will try
to indicate what I take to be its major themes." (pp. 173-174)
"This book touches on scores of topics that have not been men- tioned here, including the definition of existence, existing at a time,
relations, fictional objects, common-sense philosophy, second- order logic, mathematics, and scientific theories, plus an appendix on what the author calls
"ultralogic," which is a logic that applies correctly in all situations, even impossible ones. The discussion is often provocative and almost always
highly programmatic. Routley has explored portions of Meinong's jungle, and this edition is a fascinating diary of his journey. We still await a detailed map
of the terrain." (p. 179)
Priest, Graham. 1997. "Sylvan's Box: A Short Story and Ten Morals." Notre Dame Journal of Formal Logic no. 38:573-582.
Abstract: "The paper contains a short story which is inconsistent, essentially so, but perfectly intelligible. The existence of such a
story is used to establish various views about truth in fiction and impossible worlds-"
"Fictions are certainly not the only context in which impossible worlds—in whatever sense one takes to be correct—arise. Such worlds are
also required to evaluate the truth of counterlogical conditionals.
Another possible place in which impossible worlds may turn up is in an analysis of belief. Suppose that you were naıve enough to have
believed my story, as a child might have done. You would then have believed that Sylvan had possessed a box that was both empty and nonempty, but you would not
have believed that he had a cow that both did and did not lay eggs. If we parse ‘x believes that s’ as a relation between a
believer and a proposition, we may then take a proposition, in very orthodox fashion, to be the set of worlds/situations in which s is true.
This gives the required result.
(Despite this, I doubt that impossible worlds are of much use in an analysis of belief; actual belief seems to have no determinate logical
structure at all.)
The final point is less of a moral, more of an observation.
(10) An impossible world, as characterized above, is one where a logical truth is false, that is, its negation is true. There is nothing in
this definition that precludes the actual world from being logically impossible. (All the logical truths may still hold there.) And once one agrees that there
are impossible worlds, the question obviously arises as to how one can be so sure that the actual world is not one of them. There are, it seems to me, no good
a priori reasons to suppose that it is not." (p. 581)
———. 2003. "Meinongianism and the Philosophy of Mathematics." Philosophia Mathematica no. 11:3-15.
"Part of the beauty of meinongianism—or at least of Richard's approach to it, spelled out at length in Exploring Meinong's
Jungle —is its technical simplicity. To do the idea full justice you need to have inconsistent and incomplete worlds, but these you have anyway, at
least if you subscribe to some version of relevant logic. But the main technical trick is just thinking of one's quantifiers as existentially neutral. '∀ is
understood as 'for every'; '∃' is understood as 'for some'. Existential commitment, when required, has to be provided explicitly, by way of an existence
predicate, E , which, pace the way that Kant is often—and erroneously—interpreted, is a perfectly normal predicate. Thus, 'there exists something such
that' is '3x(E x ∧ ... x .. )'; and 'all existing things are such that' is '∀x(E x → ...x ...)'. The action of the theory is mainly,
therefore, not at the technical level, but at the philosophical level." (p. 4)
Rapaport, William J. 1984. "Critical Notice of Exploring Meinong's Jungle and Beyond , by Richard Routley." Philosophy
and Phenomenological Research no. 44:539-552.
"Exploring Meinong's Jungle and Beyond is a lengthy work (over 1000 pages) of wide scope, its cast of characters ranging from
Abelard to Zeno. The nominal star is Meinong, of course, yet the real hero is Reid.(2) Topically, Richard Routley presents us with a virtual encyclopedia of
contemporary philosophy, containing original philosophical and logical analyses, as well as a valuable historical critique of Meinong's work." (p.
"If Meinong and Reid are the heroes of this work, then the "Reference Theory" (RT) - the theory that "truth and meaning
are functions just of reference" (i) - is the villain. Routley sees his task as offering a different paradigm, noneism, which "aims at . . . a very
general theory of all items whatsoever.(5). Where RT and its classical logic fail to provide solutions to problems of non-existence, intensionality,
deducibility, significance, and context (ii), the noneist Theory of Items will - it is claimed - not only solve all of these, but also enable philosophers to
treat adequately for the first time problems from the history of philosophy (including Reid's philosophy, Epicureanism, nihilism, sophism, fatalism, the Third
Man), the philosophy of religion, the logic of perception, quantified tense logic, the problem of universals, and more (8-11). Noneism is Routley's patent
medicine for all philosophical ills." (p. 540)
There is much to admire in Routley's compilation, as well as much to ponder, to question, and to criticize. The book would have been better
had it been more coherent (in all sense of that word), but the effort required to plow through it is often rewarded." (p. 551)
(2) Cf., e.g., chap. 6, "The Theory of Objects as Commonsense," especially pp. 529 ff., and chap. 12, sec. i.
(3) See, inter alia, chap. 5, "Three Meinongs."
Seldin, Jonathan P. 1987. "A Relevant Validity in Curry's Foundations: A Reply to Richard Sylvan." Bulletin of the Section of
Logic no. 16:68-70.
"Thus, in terms of Curry’s definitions, the positive paradox principle is valid in terms of the metatheory of elementary formal systems
(which is what Curry is talking about on p. 173 of ). Curry’s claim about the
positive paradox principle is thus that it is valid in a particular context in the formal metatheory of elementary formal systems (as he has
As the last paragraph on p. 173 of  shows, he is not claiming that it is true generally." (p. 70)
 H. B. Curry, Foundations of Mathematical Logic , McGraw-Hill, New York, 1963.
Slater, B.H. 1992. "Routley's Formulation of Transparency." History and Philosophy of Logic no. 13:215-224.
Abstract: "Routley's Formula says, for instance, that if it is believed there is a man then there is something which is believed to be a
man. In this paper I defend the formula: first directly, hut then by looking at work by Gensler and Hintikka against it, and at the original work of Routley,
Meyer and Goddard for it. The argument ultimately reduces to a central point about the extensionality of objects in Routley, Meyer and
Goddard's intensional system, i.e. in its formulation of transparency."
"In 'Routley's Formula'
O(Ex)Mx ⊃ (Ex)OMx
'O' is an intensional operator on (Ex)Mx, such as 'it is believed that', and 'M' is an ordinary predicate, such as 'is a man'. So the formula
says that if it is necessary, permitted . . . known, or supposed that there is a man, it follows that for something it is necessary . . . or supposed that it
is a man. Now the formula has ground against many philosophers' intuitions. Indeed, it is invalid in all the standard systems of modal and general intensional
logic, except the epsilon calcu!us system of Routley, Meyer and Goddard (Routley, Meyer and Goddard 1974 (hereafter referred to as Routley et alii), Routley
1977). On one view of 'intensional' objects they are world-bound or mentally private objects. On that view, other minds and worlds are like other places and
times. So what is there may bear little relation to what is here.
And yet, as we shall see, the formula is true. For, on another view of the matter, if anything is on one's mind, it is a public object, and
anything in another world is bound to be in this. Certainly it need not be conceived as it is publicly, or actually, but it is definitely the same object.
Indeed the behaviour of 'it', in that last sentence, substantiates the very point which is made in it.
But many systems of logic do not capture the behaviour of such pronouns. And so doubts about Routley's Formula quite often arise. In the full
defence of the formula, therefore, it becomes especially important to consider it both formally and informally. Exactly which aspects of Routley et al's system
allow the formula to be validated, when all the others invalidate it? And does its very exceptionality, and the range of intuitions against it, not reduce its
I shall conciude, in the end, that Routley's Formii!a survives the current arguments against it, and can be given an increased rationale from
that provided when it was first defended." (p.215)
Routley. R. Meyer. R. K. and Goddard. L. 1974 'Choice and descriptions in enriched intensional languages-I'. Journal of philosophical
logic . 3, 291-316.
Routley, R. 1977 'Choice and descriptions in enriched intentional languages, II,III'. in Problems in logic and ontology (ed. E.
Morscher. J. Czermak. and P. Weingartner). Graz (Akademische Druck-und Velagsanstalt), 173-222.
Trew, A. 1968. "Incompleteness of a Logic of Routley's." Notre Dame Journal of Formal Logic no. 9:385-387.
"In 'Some things do not exist', Notre Dame Journal of Formal Logic , v. VII (1966), pp. 251-276, Routley examines the relations
between certain predicate logics. His system R* differs from the usual restricted predicate logic only in having added to it individual constants and a
predicate constant Έ ' read 'exist(s)', and in having assigned to its individual variables, a domain consisting of all possible things, in place of
the usual domain consisting of all existing things. R* has a standard theory for its quantifiers, (π, Σ)." (p. 385)
von Solodkoff, Tatjana, and Woodward, Richard. 2013. "Noneism, Ontology, and Fundamentality." Philosophy and Phenomenological
Research no. 87:558-583.
Abstract: "In the recent literature on all things metaontological, discussion of a notorious Meinongian doctrine—the thesis that some
objects have no kind of being at all—has been conspicuous by its absence. And this is despite the fact that this thesis is the central element of the noneist
metaphysics of Richard Routley (1980) and Graham Priest (2005). In this paper, we therefore examine the metaontological foundations of noneism, with a view to
seeing exactly how the noneist's approach to ontological inquiry differs from the orthodox Quinean one. We proceed by arguing that the core anti-Quinean
element in noneism has routinely been misidentified: rather than concerning Quine's thesis that to be is to be the value of a variable, the real difference is
that the noneist rejects what we identify as Quine's "translate-and-deflate" methodology. In rejecting this aspect of Quinean orthodoxy, the noneist
is in good company: many of those who think that questions of fundamentality should be the proper focus of ontological inquiry can be read as rejecting it too.
Accordingly, we then examine the differences between the noneist's conception of ontology and that offered by the fundamentalist. We argue that these two
anti-Quinean approaches differ in terms of their respective conceptions of the theoretical role associated with the notion of being. And the contrast that
emerges between them is, in the end, an explanatory one."
Priest, Graham. 2005. Towards Non-Being . Oxford: Oxford University Press.
Routley, Richard. 1980. Exploring Meinong's Jungle . Canberra: Philosophy Department Monographs, Research School of Social Sciences,
Australian National University.
Witherall, Arthur. 2000. "Lewis and Sylvan on Noneism." Grazer Philosophische Studien no. 58-59:181-202.
"Several years ago David Lewis wrote a paper titled "Noneism or Allism?"(1) in which he attacked the idea that Richard
Sylvan's (alias Richard Routley) rehabilitation of Meinong's theory of objects was truly what it was supposed to be. Lewis argued that Sylvan was not really a
noneist, and that he should be interpreted as claiming that all of the objects that philosophers consider controversial actually exist (rather than none of
them, as the name "noneism" implies). This is a drastic re-interpretation of Sylvan's work, and if it were true it would mean that he did not
successfully rehabilitate the theory of objects at all.
Unfortunately, Richard Sylvan died in 1996, without having constructed a reply to Lewis. Although it is therefore difficult to say what kind
of a reply he would have made, I believe that I can offer some significant criticisms of my own. I do not claim to represent Sylvan as such, but I claim to be
sympathetic to his project, and in this respect I can do something towards refuting Lewis' claims. This is an important defensive task to perform for a
Meinongian, because although Lewis' argument does not assail the details of Sylvan's philosophy, it threatens to restore the old orthodox view of Meinongian
metaphysics as 'committed' to an unreasonably bloated ontology, and thus to re-instate a serious misinterpretation of the whole enterprise. In assessing Lewis'
paper, it must be kept in mind that he does not address any of Sylvan's arguments . He is only concerned with whether Sylvan should be seen as a true
noneist or as an allist, with respect to the question of which controversial items exist. Nevertheless, in neglecting Sylvan's arguments, Lewis is
attention away from the substance of his position, and casting him as the defender of something unintelligible. I will show why this attack
ultimately fails." (pp. 181-182)
(1) D. Lewis "Noneism or Allism?" in Mind Vol. 99, January 1990, pp. 23-31.