HOW EPISODIC IS SEMANTIC MEMORY? 
Andrew Ortony 
University of Illinois at Urbana-Champaign 
At the end of his Philosophical 
Investigations Wittgenstein (1963) notes 
that the confusion and barrennes of 
psychology is to be explained not by the 
youth of the science but by the conceptual 
confusions that underlie it. I think one 
could easily make a case for saying that 
questions concerning the distinction 
proposed by Tulving (1972) between episodic 
and semantic memory generally involve 
precisely such conceptual confusions. What 
I propose to do in this paper is first to 
illustrate such a confusion, and then to 
suggest a possible way round it. 
Addressing the question, "Is there a 
semantic memory?", Schank (1974, 1975) 
argues that there is not. Semantic memory, 
he claims, has been treated by psychologists 
as being made up of words and relationships 
between them, and has been proposed as a 
means of representing both the meanings of 
sentences and the knowledge required to 
understand them. This he believes is wrong; 
what we should actually do is to separate 
out a language-independent aspect, call it 
conceptual memory, distinguish it from 
lexical memory, and identify it with 
episodic memory because the.relationships 
between concepts in it "could only have been 
acquired by personal experience." 
Consequently the distinction between 
semantic and episodic memory disappears, 
which is all to the good since semantic 
memory is an ill-conceived notion. 
The first confusion in this position is 
factual rather than conceptual. It is 
simply not the case that psychologists who 
have worked on semantic memory proposed it 
as an associative network of words. All the 
workers cited by Schank explicitly deny this 
in their work. The distinction which he 
wants to make, while valid enough in itself, 
is implicit in all existing models, and is 
quite explicite in the most recent 
formulation of Quillian's model proposed by 
Collins and Loftus (in press), where 
allowance is made for a distinction between 
lexical and conceptual associations, just as 
Schank proposes. It is clearly a mistake to 
confuse knowledge of words with knowledge of 
word meanings. In all models the role of 
the dictionary on lexicon or lexical network 
is to represent knowledge about words which 
is not primarily semantic, but, to quote 
Collins and Loftus: "...is organized along 
lines of phonemic (and to some extent 
orthographic) similarity." 
Schank believes that semantic memory 
(excluding lexical memory) doesn't exist, 
and it seems that one of his chief reasons 
for this belief is that the contents of 
semantic memory are acquired through 
personal experience. Now Schank might be 
right that the semantic/episodic distinction 
is not worth very much, is not useful, is 
misleading or whatever, but that the set of 
associations and other relations represented 
in a language-independent memory "could only 
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have been acquired by personal experience" 
is quite irrelevant, in a sense, probably 
false, and certainly does not justify the 
conclusion that Schank draws, namely that 
"conceptual memory is episodic in nature." 
The distinction envisaged by Tulving 
was not one which could be invalidated by 
merely claiming a position of extreme 
empiricism. Tulving expressed the 
distinction as that between a kind of mental 
thesaurus, and an autobiographical record of 
temporally-dated events. Generaly speaking 
memory modellors have not made much use of 
the distinction. Quillian (1968, 1969), 
Rumelhart and Norman (1973) and Anderson and 
Bower (1973), for example, all seem, in 
fact, to adopt the position advocated by 
Schank precisely because they make no sharp 
distinction between repressentations of 
sentence meanings and of world knowledge 
required for understanding. The most 
notable exception is Winograd (1972) who 
maintains a separate record of the discourse 
to help with handling anaphoric references. 
It is widely believed that semantic 
memory is characterized by rigid 
hierarchical structures giving special 
prominence to the notion of superset. Once 
one makes this assumption it follows rather 
quickly that there are defects in the notion 
of semantic memory because it cannot handle 
a variety of problems which appear to 
originate from a rigidly hierarchically 
organized knowledge base. It is, I think, 
in this line of reasoning that the first 
confusion hides. Yet, all that follows 
from, for example, the observation that 
people cannot rattle off the fifty states of 
the union is that they don't have all of 
them equally accessible from the concept of 
state; it says nothing about semantic versus 
episodic memory. Nor, incidentally, does it 
show that the superset relation is 
useless -- rather, it shows that there may 
be a limited number of readily accessible 
inverse superset relations, or exemplar 
relations. 
Schank rightly objects that using a 
rigidly hierarchical system and storing in 
it "plunger," "hammer" and "saw" 
indiscriminately under a node for "tool" 
fails to represent the greater semantic 
closeness between "hammer" and "saw" than 
between one of them and "plunger." His 
solution is to replace one static 
representaton with another, so that while 
his representation captures that greater 
proximity between "hammer" and "saw", it 
fails to represent the similarity of 
"hammer" and "plunger" that might be 
relevant in a context involving tools with 
(relatively) long handles. If we want to 
capture semantic similarities of this kind 
we should not attempt to choose one static 
representation in preference to another. 
Rather we should be prepared to allow 
comprehension and retrieval processes to 
help out. One such candidate is a spreading 
activation model (c.f. Collins & Loftus, in 
press; Ortony, 1975); a model which allows 
activation from various sources 
(specifically input string and context) to 
summate and activate concepts which might 
not have been activated above threshold by 
one source alone. If one makes assumptions 
such as these about the processes that 
operate on the structures, it can be readily 
seen that one need not worry too much about 
which particular static representation one 
utilizes in memory. Probably there is 
little to choose betwen them. Providing we 
have ~ way of representing all the 
information pertinent to a concept that we 
need, activation levels, associative 
strengths and criteriality can be invoked by 
appropriately defined processes to pull out 
those relationships which dominate in 
particular contexts. It might well be that 
the particular structures that represent 
what people know depend for their relational 
characteristics not so much on rules for the 
construction of canonical forms as on the 
particular details of the individual's 
experience. Thus a man who consistently 
uses forks to open cans might be expected to 
have his concept of fork unusually closely 
associated with his concept of can-opener 
(if he has one). Viewed this way, it would 
seem that one man's plunger might indeed be 
another man s hammer; a possibility which 
should not be ruled out by imposing 
arbitrary structural constraints. 
Being flexible and being arbitrary are 
not the same thing. Sometimes, of course, 
one can be both. A case in point is 
Schank's conception of context. On the one 
hand it seems to be merely a 
conceptualization, for the only links 
permitted within a context are those of 
conceptual dependency plus the causal links. 
On the other hand "there is a sense in which 
all of memory can be considered to be one 
big context." With a notion of context which 
is so flexible it is difficult to see what 
purposes it serves. Schank wants to say 
that "going to a museum in Berlin" and 
"going to a museum in Boston" is an example 
of an intra-context association, while 
"going to a museum in Berlin" and "going to 
an old hotel (in Berlin?)" is an example of 
an inter-context association. The reason is 
that the former pair are simply examples of 
"going to a museum" episodes whereas the 
second pair are only related because of 
"shared properties." But one might as well 
argue that "hotel going" and "museum going" 
are within the same context because they 
both fall within the general paradigm of 
"things I do when I'm away from home," or 
"visiting strange or interesting buildings." 
There simply are no compelling reasons to 
make the distinction that Schank is 
searching for on the basis of context-shlfts 
of the kind he describes. The confusion 
which I think underlies this reasoning is 
further exemplifed by the analysis of the 
protocols of his daughter, Hana. Schank 
wants to argue that Hana doesn't Jump around 
between contexts, yet in the context of 
birds flying Hana jumps to "plane" because, 
Schank says, planes fly too, but that is 
just a case of shared properties on Schank's 
own analysis, so it must, after all, 
constitute traversing an inter-context llnk. 
Nobody would deny that there are some 
very serious problems to be dealt with 
concerning the structure of knowledge and 
56 
the processes that operate on them. There 
are serious problems concerning context. 
There is no doubt that in different contexts 
different relationships and semantic 
connections between concepts are going to be 
relevant to comprehension and memory (c.f. 
Anderson & Ortony, 1975). There is also no 
doubt, as Woods (1975) points out in his 
excellent paper, that memorial 
representatons are going to have to be both 
intensional and extensional \[2\]. Current 
models have yet to make this distinction 
although it is quite obvious that one must 
keep distinct representations for noun 
phrases derived from predicates, and for 
names. Not very recently the distinction 
between Richard Nixon (extension) and The 
President of the United States (intension) 
became quite self-evident. Ortony and 
Anderson (1974) describe an experiment in 
which subjects showed a marked tendency to 
make recognition errors depending on whether 
the noun phrase in a study sentence required 
an intensional or extensional 
interpretation. 
Considerations such as these are 
Certainly important in modeling memory, but 
they do not relate to the semantic/episodic 
distinction in any obvious way. It is 
important to know which problems go 
together, and to know how and why (that is 
the beauty of Woods" paper). I think that a 
distinction between episodic and semantic 
memory is also important, not because of 
tenuous connections to problems of knowledge 
representation but because of more global 
considerations concerning the nature of 
knowledge. Before exploring this in more 
detail, however, let us clarify what is 
supposed to be distinguished from what. A 
distinction between episodic and semantic 
memory represents a difference not so much 
between different kinds of memory but 
between different kinds of knowledge in 
memory. It is the contents of memory that 
we distinguish, not the memory itself. 
What I am going to suggest may seem to 
some not to be a distinction between 
semantic and episodic memory at all. On the 
other hand I think it captures some, at 
least, of what Tulving intended and is a 
useful and important distinction for AI and 
psychology alike. 
The currently fashionable rejection of 
the notion of an episodic/semantic memory 
distinction seems to be based on the idea 
that since everything we know, we know from 
experience, ther? is little point in and no 
room for the distinction. Here lurks 
another conceptual confusion -- a confusion 
of knowledge from experience with knowledge 
of experience. Philosophers have long 
argued that although all knowledge might 
arise from experience it is not necessarily 
all given in experience. 
Consider the difference between a 
personal diary and an encyclopaedia. 
Typically an encyclopaedia contains 
information about a great variety of 
topics -- or concepts. Information in an 
encyclopaedia constitutes knowledge about 
the concepts entered in it and consequently 
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can be used to make inferences involving 
them. A personal diary, on the other hand, 
constitutes a different kind of 
knowledge -- knowledge about the individual 
whose diary it is. It would be possible, no 
doubt, to produce an encyclopaedia from a 
personal diary, but it would take a lot of 
work, a lot of inference and a lot of 
assumptions. What I want to suggest is that 
the knowledge in semantic memory can be 
thought of as the kind of knowledge which 
one would find if one were to produce an 
encyclopaedia from his personal diary. It 
is knowledge which has been reorganized 
around concepts from knowledge originally 
encoded around events. It has the further 
characteristic that it is not embedded in 
propositional verbs; it has been freed from 
their bonds by using inferential heuristics; 
it contains knowledge which can be 
represented by such propositions as "All 
bachelors are unmarried," "Most swans are 
white," etc. We all have knowledge of this 
kind, but we couldn't possibly have acquired 
knowledge about all bachelors or even most 
swans by personal experience. Of course, 
there was a personal experience involved 
when the putative knowledge was acquired, 
but precisely this is the distinction we 
must make. Probably I read in a book that 
all bachelors are unmarried (a dictionary 
perhaps). So there was a personal 
experience to the effect that "I read in a 
dictionary that all bachelors are 
unmarried." But we cannot identify the 
knowledge that we learned x under such and 
such circumstances, with the knowledge x, 
stripped of source and circumstances. What 
our teacher tells us, or what we read only 
licenses us to claim that we know that our 
teacher told us, or that we read 
something -- it does not, alone, license us 
to know, as true, what it was we heard or 
read. So, while all input can be tagged as 
to source, semantic memory somehow 
represents the untagged information, and 
that untagged information is not a record of 
personal experience. It is a record of 
personal experience stripped of whatever 
makes it personal. It is derived from 
personal experience but does not represent 
it. It represents, as it were, knowledge 
without the guarantee. 
Some years ago BBC TV showed a program 
in which was described the growing of 
spaghetti on spaghetti trees in the south of 
Italy. Most of us would probably reject 
this notion as an absurd fabrication, but 
not so for all the viewers; some "took it 
seriously." A proposition describing the 
personal experience might be something like 
"I saw a TV progrm which alleged that 
spaghetti grows on trees," which we can 
write as "I saw S'" where S" itself can be 
represented as "A TV show allege(d) that S" 
and where S represents the proposition 
"Spaghetti grows on trees." 
The role of episodic memory in my sense 
is to store a record of the experience in 
the general form "I experienced S'". My 
contention is that believers and 
non-believers of the spaghetti story alike 
would have stored some such representation, 
namely a representation of S" tagged with 
autobiographical information such as 
modality of input, relative time and so on. 
Except perhaps for acidheads and avid 
Cartesians, most of us are willing to trust 
our senses most of the time -- we are 
willing, that is, to infer S" from "I saw 
S'", but S" still contains source 
information. Focus now on the knowledge 
representable by the proposition, S, 
"Spaghetti grows on trees." If we were to 
incorporate this piece of knowledge in the 
data base it could be used in all kinds of 
inferences about spaghetti (the crop depends 
on climate, the cost of harvesting it may 
vary, it is a fruit or vegetable, etc.). 
However, in general there is no simple way 
of inferring S from S" and certainly no such 
inferences about spaghetti can be made from 
S" alone. The role I want to attribute to 
semantic memory is that of a repository of 
knowledge with the characteristics of S, 
knowledge, that is, which has been stripped 
of its autobiographical reference, and its 
source and circumstances of acquisition 
information too; always the result of 
inference. 
Those of us who realized that the 
spaghetti sequence was just another skit 
from the satirical program Monty Python's 
Flying Circus did not encode something like 
S in semantic memory -- at most we encoded 
or represented something like S" which 
represents source-free information or 
knowledge about a TV show but does not 
represent source-free spaghetti information! 
Those who were duped, on the other hand, 
stripped S" of its source and circumstances 
and represented the knowledge expressed by 
S. Thus knowledge in semantic memory is 
derived from, but fundamentally different 
from knowledge in episodic memory. Putative 
knowledge which is potentially semantic 
always arrives embedded in episodic 
knowledge; it can always be represented as 
being governed by a propositional verb. 
I know a lot of things about England 
and a few things about Lord Nelson. One of 
the things about Nelson that I know is that 
he said "England expects every man to do his 
duty," but that is not one of things I know 
about England. England's expectations were 
either never sufficiently relevant or never 
sufficiently true for me to have freed them 
from Nelson's claims. The knowledge that I 
have about Nelson may be in semantic memory 
because it is free from the bonds of its 
source -- in forgetting the source I may 
have assumed it to be true -- but it only 
gets into semantic memory if it is assumed 
to be true (enough). 
I earlier urged that semantic memory is 
centered around concepts and that episodic 
is centered around events. I think there is 
a sense in which episodic memory is centered 
around a concept, the concept of "self". If 
I were to become famous, many of the things 
in my personal diary might be entered in an 
encyclopaedia under an entry for me. 
Personal experiences are all the experiences 
of an individual and since there has to be a 
concept of self in memory one might argue 
that episodic memory is merely the structure 
of knowledge associated with the concept of 
57 
the individual. Such a conclusion I find 
quite unobjectionable. It suggests that all 
input and output is mediated through a 
concept of the self. Input, initially 
represented there, may be transferred to 
other concepts under certain conditions 
thereby freeing it of its autobiographical 
reference (that doesn't necessarily mean it 
gets automatically destroyed in its original 
form). Output can be represented as "I said 
that..." or by some other performative verb. 
It is interesting that a characteristic 
feature of generative semantics is that all 
sentences are dominated by a verb 
representing the speech act -- such a view 
is of course quite a natural consequence of 
the prominence that I am suggesting be 
attached to the concept of self. 
There are a couple of other reasons 
which incline me to support this 
distinction. First there is a mass of 
experimental research on encoding 
specificity which strongly suggests the need 
for some such distinction (see, for example, 
Watkins & Tulving, 1975). Secondly there is 
the rather mundane observation that we 
frequently come across people who have "bad" 
memories. The problem with such people is 
not that they have inferior, or diluted 
knowledge-bases -- they are not lacking in 
knowledge. Their problem is the maintenance 
of a record of personal input/output 
experiences. They tend to absorb what they 
consider important, they are perfectly able 
to learn, but they can't remember where they 
put their car, or to whom they lent a book, 
or from whom they heard something. If all 
semantic memory were episodic, they would 
have to be stupid as well as forgetfull 
There remains (as always) a number of 
unanswered questions if one takes this 
approach. The most important one, of 
course, is how and when does information get 
into semantic memory, and how and when does 
it get lost from episodic memory. Answers 
to these questions are beyond the scope of 
this paper, but some speculations at least 
about the first might start things off. In 
order to infer S from S" inference based on 
some or all of the following considerations 
will have to be made: Is it relevant? This 
suggests that not everything we experience 
is worth recording in semantic memory (what 
I ate for dinner on some arbitrary day, for 
example). How reliable is the source? If a 
three year old child tells me that all men 
are daddies I may find it relevant to what I 
need or want to know about the child, but I 
am not likely to trust him as an information 
source about universal qualities of men. To 
what extent does it conflict with what I 
already believe? The child's claim faces 
another problem on this score. One must 
assume that the knowledge base can tolerate 
some degree of inconsistency, but as Quine 
(1952) suggests, some things may be much 
more difficult to give up or revise than 
others. Relevance or criteriality indices 
will handle this, together with degrees of 
truth. Is there independent corroboration? 
If some putative fact or procedure seems, on 
the basis of what is already known, very 
unlikely to be true, independent evidence 
for it may boost its degree of truth for me. 
5B 
There are doubtless other considerations 
(many can probably be gleened from the 
belief and attitude literature) but the 
general point is that an assessment of a 
degree of belief has to be made. If a 
threshold is reached the thing has some 
positive degree of trutlh and can be stripped 
of the source and circumstance information 
(perhaps with some modification), and once 
this is achieved all is in order to free it 
from its bound form and to treat it as a 
bone fide piece of knowledge to be 
incorporated into the existing structure in 
semantic memory. Clearly an analysis of 
speech acts will be required since the rules 
for freeing the putatiwe knowledge will be 
different for performatves such as 
"convince", "promise", "prove," etc. 
The problems that we face are difficult 
and complex. I am confident that they can 
be solved, but I am equally convinced that 
to solve them in a satisfactory way is going 
to require that our models develop from 
ideas which are both eplstemologically and 
psychologically sound. I have tried in this 
paper to put forward some arguments and to 
develop some ideas towards this end. 
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