Review of The Proper Treatment of Events |
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Date: Thu, 18 Aug 2005 09:24:38 -0700 (PDT)
From: Magda Dumitru
Subject: The Proper Treatment of Events
AUTHORS: van Lambalgen, Michiel; Hamm, Fritz
TITLE: The Proper Treatment of Events
SERIES: Explorations in Semantics
PUBLISHER: Blackwell Publishing
YEAR: 2005
Magda Dumitru, unaffiliated scholar
SUMMARY
The volume comes fourth in the series "Explorations in Semantics"
edited by Susan Rothstein, and dedicated to students and
researchers in linguistics and philosophy of language. It has three
parts, the first on linguistic issues ("Time, Events, and Cognition",
comprising chapters 1, 2, and 3), the second on computational and
logical formalisms ("The Formal Apparatus", including chapters 4, 5,
and 6), and the third on their "marriage" ("A Marriage Made in
Heaven -- Linguistics and Robotics"- chapters 7 through 12). An
Appendix, "The Basic of Logic Programming", is last to follow.
The semantics of tense and aspect is studied from the vantage point
of cognitive science (truth and reference are cognitive, not real
entities; tense and aspect are discussed in terms of goals, actions and
consequences) and is approached in a fully computational way with
clear pedagogical intent -- exercises are proposed at the end of
several chapters, and the reader is addressed directly: "Readers not
familiar with this notion are advised to read the Appendix first" (p.
51); "The reader for whom this is all new is advised to read only the
statements of the theorems and skip the proofs" (p. 58); "the reader
who is having trouble here is advised to refer back to that section" (p.
108); "it would be clear (at least to a mathematically inclined reader)
what to do" (p. 223). An errata, supplementary material (proofs), and
slides for eventual instructors can be found at
http://staff.science.uva.nl/~michiell.
Chapter 1 "Time"
The main question the authors ask is: 'what must our minds be like for
tensed talk to make sense?'. Their answer is that human minds
manage to integrate past, present, and future via planning
(constructing and prioritizing events in memory). Therefore, temporal
perspective ought to be the main conceptual view on time, from which
other views (time as duration and time as succession) are derived.
Goal-plan knowledge can relate past, present, and future when
constructing narratives (executions of plans toward given goals), for
instance, via episodic memory -- defined as a "generalized capacity
for imagining or constructing possible worlds" (p. 13). The authors
adduce psychological and neurological evidence supporting their
conclusion.
Chapter 2 "Events and Time"
The chapter is meant to better define the notion of event, from a
cognitive point of view: "the basic building block of the human
construction of time is the event" (p. 15). Semantics, defined as
cognitive representation of events, must include both temporal and
non-temporal relations; the latter involve goals and actions
undertaken to achieve them, as well as cause and effect. An example
discussed here is the French Passé Simple (PS), which may refer
either to an event taken as a whole, or to its left and right boundaries.
The authors further favor the Walker construction of events, instead of
the Russell-Kamp model, because it is able to better account for the
semantics of the PS, and because it has other important features: it
allows for instants to be directed and to mark change, it assumes the
notion of spacious present, and insures the derivation of continuous
time from events. Humans individuate events (and hence construct
time) by using object recognition (by distinguishing figure from ground)
and by forming goals and plans (the raising of a hand may be part of a
handshake or of a grasping action).
Chapter 3 "Language, Time, and Planning"
Language production may be linked to planning via linearization.
Moreover, planning is instrumental in establishing discursive
coherence via anaphoric and temporal binding. The authors maintain
that tense itself should be interpreted in discourse, not in single
sentences (issue taken to be a counterargument to generativism). An
example supporting this argument is, again, the French PS, proven to
introduce events into discourse, which are then ordered thanks to
world (causal) knowledge. Planning plays an important role in
semantics: English future tenses involving auxiliaries always encode
goals; human cognition seems to be goal-oriented, since the perfect is
future oriented (the reference time lies in the future of the event time --
following Reichenbach); "Language production can be characterized
as transforming a semantic structure" (p. 27).
Chapter 4 "Events Formalized"
The chapter discusses event calculus (EC), a formalism for planning --
nonmonotonic (default) reasoning -- involved both in time cognition
and tensed language. EC requires a first-order logic whose
vocabulary includes individual objects, real numbers (to represent
time), time-dependent properties (states and activities), variable
quantities, and event types (marking the limits of time-dependent
properties). EC allows for reification/ nominalization (properties may fill
an argument slot in a predicate); perfect nominalizations are
temporally related (are modeled as event types), whereas imperfect
nominalizations are modeled as fluents and are not temporally related.
EC also allows for predicates to include an explicit parameter for time.
As for tenses, the past applies to events, whereas progressives apply
to fluents. Causality, a relation between events, is taken to belong to
physics and comes in two varieties: instantaneous change and
continuous change. In instantaneous change, event types (e.g.
collision) may become event tokens by combining with a time
parameter. Event types are initiated or terminated by a fluent (fluents
are time-dependent properties -- sets of intervals including initiating
and terminating instants; fluents are considered as both functions and
objects, which may further take a parameter x). Relevant predicates
are 'Initially', 'Happens', 'Initiates', and 'Terminates'. In continuous
change (e.g. drinking a glass of wine) the relevant
predicates 'Trajectory', 'Releases', 'Clipped', 'Declipped', and 'HoldsAt'
insure that some properties ('f-relevant events') escape the inertia
specific to the first form of causation; "continuous change occurs due
to a force, not an event, and hence absence of relevant events does
not always entail absence of change". The definition of events
includes the 'Happens' predicate, while the definition of fluents
includes the 'HoldsAt' predicate.
The long-standing semantic issue of whether fundamental temporal
entities should be points or intervals is thus sidestepped; the authors
maintain that events and fluents, both extended in time yet playing
different roles in EC, are fundamental temporal entities. Robotics
needs to derive predictions, and therefore insures situation
description via axioms (holding for every situation) and scenarios
(holding for a particular situation). Inertia ought to be defined by a
suitable logic, working alongside EC and restricting the class of
models. Computational limitations lead the authors to operate with
minimal models exclusively (defined as 'closed worlds' including only
events and causal influenced between events, as specified for a given
scenario), not with substructures of the 'real', as Discourse
Representation Theory does, for instance. Developing discourse is
modeled as a nonmonotonic progression (as a form of planning),
which accounts for the meaning of the progressive in English and for
the phenomenon of coercion.
Chapter 5 "Computing with Time and Events"
"if semantics wants to make contact with the huge psycholinguistic
literature on language comprehension and production, it had better
become computational" (p. 49). Accordingly, the authors adopt
Moschovakis' idea that the sense of an expression identifies with the
algorithm that computes the denotation of that expression. The
authors also cite evidence by Mani and Johnson-Laird, according to
whom uniquely determined cognitive models facilitate the recall of a
piece of discourse, and hence could be stored in memory. Models
(which include denotations) are computed by the sense of
expressions. The semantic theory proposed includes two languages:
a language of predicates in EC, and a language of constraints
(formulas). Both languages define a programming language:
constraint logic programming, which differs from standard logic
programming in that unification proceeds via equation without
substitution. The logic program consists thus of a scenario and the
axioms of EC. A minimal model of the logic program is defined as the
completion of the program.
Chapter 6 "Finishing Touches"
Nominalization is taken to be instrumental in the construction of tense
and aspect, since "nominalized VPs are the basic units of semantic
computation, in their guise as fluents and events" (p. 71). Montague
semantics, dynamic semantics, and Davidson's analysis of events are
all rejected as possible bases for analysis for different reasons: the
first treats intensions via possible worlds, the second treats
computation at an abstract level, and the third is not representing "an
extensional two-sorted first order language in which predicates may
have a time parameter" (p. 72). Events and fluents, not language
formulas, are the basic computational entities, since they are involved
in causal relationships.
Chapter 7 "Aktionsart"
"Aktionsarten form a continuum, organized around five prototypes,
rather than a discrete set" (p. 93). An Aktionsart is not "a permanent
feature attached to a V or a VP" (p. 83), since verbs can be coerced
into any Aktionsart. Aktionsarten are seen as eventualities(in the
sense of Emmon Bach) attached to a VP, and defined as a quadruple
containing an event and up to three fluents. An eventuality determines
a scenario by specifying the meaning of the elements present in the
quadruple. Verbs are of the form run(x, t), where x is the subject
position, and t the time parameter, over which it can be abstracted in
two ways (as an event type -- which is a function of time, and as a
fluent -- which is an object), yielding perfect and imperfect nominals.
Users don't have direct access to the time parameter, yet do have
direct access to derived event types and fluents, represented
as "definable finite unions of intervals and points" (p. 88). Tense,
expressed by the predicates 'Happens' and 'HoldsAt', applies once
the abstractions obtain. The imperfect paradox is solved by
dissociating the goal (incremental theme) from the activity leading to
that goal, which are then fused together in a single event.
Chapter 8 "Tense"
The formalization proposed for tense makes reference to the concept
of 'integrity constraints', borrowed from database theory, and
expressing "obligations and prohibitions that the states of the
database must satisfy if they fulfill a certain condition" (p. 99); when
updating a database, care must be taken for these integrity
constraints to hold under the new circumstances. Mostly event types
(hence eventualities viewed perfectively) are located in time (either in
a given event structure or in their representation as instants or,
ideally, on the axis of the reals). Reals are needed to represent
aspect. Cognition works with both event- and instant structure. The
starting point for representing time is Reichenbach's tripartite structure
(reference time R, event time E, and utterance time S). R is defined as
an "integrity constraint formulated in terms of fluents, which typically
puts constraints upon possible temporal locations of event types,
including the events [fluents and event types] constructed by
hierarchical planning" (p. 103). Integrity constraints help define truth
for tensed sentences, in the sense that sentences are true if the
integrity constraint is satisfied, and false otherwise. R is taken to be
fundamental, since it is fixed by an integrity constraint, and represents
an anchor for E. The (semantic) present tense takes R, E, and S to
coincide. The past tense situates both R and E before now; it
operates on an event type (e.g. running, writing, etc.). Unlike the
perfect, the past tense requires an explicitly established past
reference point. The past progressive applies to an event fluent and
does not entail the completion of the event type, unlike the past tense.
The author's aim is to define tense for each Aktionsart separately;
however, when applying the progressive to Aktionsarten other than
activities and accomplishments, the scenario must be extended in
order to coerce the VP to either an activity or an accomplishment.
Future events can be conceptualized as events per se, or as goals
(through the use of the auxiliary 'will', the 'be going to' VP, and the
futurate progressive).
Chapter 9 "Tense in French: Passé Simple and Imparfait"
The chapter sketches the semantics of the French Passé Simple and
Imparfait, as an application of the machinery developed in the
previous chapters. Of particular interest is the ordering of events in
time described by the PS; the authors maintain that the ordering can
be established by computing the meaning of the PS sentences,
together with world knowledge, and anaphora relations. PS obeys an
integrity constraint such that an eventuality is represented as
perfective and located in the past; however, PS itself cannot insure
ordering relations by itself. As for the Imparfait, it obeys an integrity
constraint such that it becomes represented as an "anaphoric,
imperfective past tense" (p. 136). This is supplementary evidence
against analyzing sentences in isolation.
Chapter 10 "Grammatical Aspect"
The perfect is taken to belong to the category of grammatical aspect,
and therefore it "sits uncomfortably between the two stools of tense
and aspect" (p. 151). The present perfect includes, in its meaning, the
idea of current relevance of an event, while the reference time is set
at 'now'. The past perfect either provides a past reference time while
its consequences still hold, or it is only a past in the past. The integrity
constraint at work for the present perfect introduces a time at which
the start event happens. The progressive is coercing an expression
into either an activity or an accomplishment; moreover, the authors
argue for a third truth value (indeterminate) for cases such as
the 'Multiple-Choice Paradox', yet offer no convincing arguments.
Chapter 11 "Coercion"
Since 'Aktionsart is not fully determined prior to the sentence level' (p.
168), aspectual coercion insures that constructions such as the
progressive force a VP to change aspectual category. The authors
describe three types of coercion: additive, subtractive, and cross-
coercion, which mean, respectively, that a given scenario is built (by
adding a direct object to a verb, for instance), that parts of a scenario
are deleted, or that parts of a scenario are unified (a constant and a
parameter, for instance). An interesting issue is the representation of
nominals: "In our setup, the denotation of a house is as it were
distributed over the changing partial object, the canonical terminating
event, and the consequent state whose relations are governed by the
scenario" (p. 177). In passive sentences, where NPs move to the
subject position, the nominal may be reinterpreted as a real object
(and hence adjectives can be applied). The authors assume that
aspect imposes temporal structure on events and therefore may
override the Aktionsart of a verb. The process is made possible if one
interprets Frege's notion of sense as a basis for determining
reference; otherwise the authors consider events not to have any
canonical referents in the world. The sense of an expression is its
associated scenario; one may navigate between the senses an
expression may have by appealing to coercion.
Chapter 12 "Nominalization"
Although the authors concede that 'Nominalization is a very
complicated phenomenon" and that "we can barely scratch the
surface here" (p. 207), they begin the analysis with a distinction
Vendler once made, between two kinds of verbs: 'loose containers'
(e.g. surprised us, is unlikely, is improving), and 'narrow containers'
(e.g. took place yesterday). Loose containers take both nominal and
verbal gerunds (corresponding to perfect nominals -- event types --
and imperfect nominals -- fluents, respectively), while narrow
containers take only nominal gerunds. Coercion may explain this
asymmetry, if it is assumed that there are two kinds of nominals
(eventive and factive), and that an eventive noun is reinterpreted as a
factive noun when combined with a loose container. The chapter then
presents a historical view on the English gerundive system, in order to
highlight the origins (phonological and morphological processes) and
function of the verbal gerund (a newer type of gerund that came to
function alongside the old type -- the nominal gerund). The authors
agree with theories such as Houston's, according to which verbal
gerunds (and participles) used to have mostly an adverbial function
and introduce background information; therefore verbal gerunds are
taken to introduce fluents.
The authors then propose a formalized theory of nominalization based
on Feferman calculus, as follows: a perfect nominal (atemporal) can
be created from a verb by suppressing its temporal parameter through
existential quantification. On the contrary, imperfect nominals can be
internally modified by tense and aspect, since the temporal parameter
of the underlying verb is abstracted. Interestingly, the actual lexical
content of perfect and imperfect nominals is of no consequence here.
Determiners are taken to encode tense; event types in the restrictor
are related to event tokens in the nuclear scope. Coercion regulates
both the nominal and the verbal systems, considered to be
interdependent. The abstract structural representation of perfect and
imperfect nominals can be enriched with lexical content (determined
by a scenario) and Aktionsart of underlying verbs; together, they form
a temporal profile, further interacting with verbal context.
CRITICAL EVALUATION
The volume has important qualities: it is very interesting and thought
provoking, especially for linguists (although language engineers and
philosophers may profit as well). It is an attempt at bridging the gap
between artificial intelligence and linguistics in a consistent way, by
discussing various core issues, such as time, tense, aspect, verbal
and nominal categories, and category shifting (coercion). They all
involve events, in some way or another, hence the title 'The proper
treatment of events' would seem justified, though less suggestive of
the wealth of topics discussed throughout the book.
As far as editing is concerned, it looks like the book was prepared for
publication under considerable constraints of time and space. The
style is very uneven -- part I anticipates, sometimes in great detail,
conclusions and implications of the theory to be proposed and
applications to be discussed later in the book; part II is rather terse,
since much information is presented in very little space; part III is
considerably more elaborated, sometimes too much so -- the detailed
historical account of the English gerund, although very interesting, is
not justified by the economy of the book, especially since the authors
seem to bear it in mind -- 'Giving the full completion of the program
would take up too much space' -- p. 62; 'Unfortunately, for lack of
space, we will not discuss the very important topic of argument
structure' -- p. 72; 'It is however a nightmare from the expository point
of view to have to work with both an event structure and its
representation as a continuum' -- p. 98, etc. Economy may also be the
reason for not providing translations for the French example-
sentences.
Other 'slips' seem to be the result of haste -- sometimes, symbols are
not defined as soon as they are introduced ('r' at p. 40 is explained at
p. 72; the 'imperfective paradox', first mentioned at p. 44 is discussed
at p. 156,etc.), etc.; this little problem could be solved by introducing
addenda. Typos are rare: 'morphologial' -- p. 151; 'as the long as' -- p.
219 etc.
Psychological and neurological evidence cited mostly in the first
chapters may be interpreted as supporting the view that humans are
goal-oriented agents. The authors infer from it that humans ought to
apply the same cognitive mechanisms when approaching language
(grammar): "It is then but one step to hypothesize that the linguistic
coding of time is also driven by the future-oriented nature of our
cognitive makeup". The 'step' may be very big indeed, since humans
do not seem to root their goals in the present exclusively
(Reichenbach's model may not be complex enough for a cognitive
approach), despite the way future is encoded; also, it is not sure
whether being future-oriented always means being goal-oriented.
However, such considerations might link to the assumed linearity and
first-order approach of the book, and hence may be seen
as 'necessary evils'.
As for the celebrated "marriage" between linguistics and robotics, it
does not resemble very much a union, but rather a unification, where
computation seems to be what all this is about, were it not for integrity
constraints: sense is defined as an algorithm leading to meaning
(denotation) as given by a minimal model. Perhaps a detailed
theoretical discussion here would have been too much to ask from
such a dense book.
Last but not least, the authors cite a rich bibliography that, together
with the pedagogical e-tools and the wealth of ideas suggested
make 'The proper treatment of events' an essential book for linguistics
students and researchers interested in the latest trends.
REFERENCES
Davidson, D. 1967. The logical form of action sentences. The logic of
decision and action, ed. by N. Rescher. Pittsburgh, PA, University of
Pittsburgh Press.
Feferman, S. 1984. Toward useful type-free theories. Journal of
Symbolic Logic, 49, pp. 75-111.
Frege, G. 1962. Sinn und Bedeutung. G. Frege: Funktion, Begriff,
Bedeutung. Funf logische Studien, ed. by G. Patzig. Goettingen,
Vandenhoeck.
Houston, A. 1989. The English gerund: Syntactic change and
discourse function. Language change and variation, ed. by R. Fasold
and D. Schiffrin. Amsterdam, Benjamins.
Kamp, H. 1979. Events, instants, and temporal reference. Semantics
from different points of view, ed. by R. Baeuerle, U. Egli, and A. von
Stechow, pp. 27-54, Berlin, Springer Verlag.
Mani, K. & P. N. Johnson-Laird 1982. The mental representation of
spatial descriptions. Memory and Cognition, 10, pp. 181-187.
Moschovakis, Y. 1993. Sense and denotation as algorithm and value.
Lecture Notes in Logic, ed. by J. Oikkonen and J. Vaananen, Natick,
MA, A.K. Peters.
Reichenbach, H. 1947. Elements of symbolic logic, London, Macmillan.
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ABOUT THE REVIEWER:
ABOUT THE REVIEWER
Magda Dumitru studies issues in Micro-Semantics, relating to
definiteness, genericity, tense and aspect.
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