: " :i .. :,-.:: . : : - . , : . • .. : i i ;!,: : . • . : ... • • i " " : • . '... • .......... .. • .. ---":t .7:g~~ :::: :i ¢ompu aI cma • . • . .. • " .: : " " " • " : ; . i • ~i: : 1"5." ... • . • .. .: :. .'~ ~.. .: • . : , : • :-: ; ;: i A. G. OETTINGER, Editor ELIZA A Computer Program Tile object of this paper is to cause just such a re- evaln~tion of the program about to be "explained". Few } 4 For the Study of Natural Language programs ever needed it more. 7:~.S C: Communication Between Man ELIZA Prograrn } ELIZA is a program which makes naturM hmguage And Machine conversation with a Colnputer possible. Its present imple- 5)~.;. ~~- ! mentation is oa the MAC time-sharing system at MIT. i: o ,JosEPh ~VEIZENBA UM It is written in 5lAD-SLIP [4] for the IBM 7091. Its name 7?27 E was chosen to emphasize that it nmy be incrementally Massach.usclls [nshl-ute qf Tcchnu[ogg,* Cambridge, Mass. :2:~: improved by its users, since its language abilities may be continually improved by a "teacher". Like the Eliza 0! 7~9j ~ ELIZA is a program operating within the MAC time-sharing Pygmalion fame, it (ran be made to appear even more system at MIT which makes certain kinds of natural language civilized, t,he relation of appearance to realiW, however, conversation between man and computer possible. Input sen- remaining in ~he donmin of the playwright. tences are analyzed on the basis of decomposition rules which For ll~e present purpose it is sufficient to characterize :7;2: Y :? are triggered by key words appearing in the input text. the ~[A() system as one which permits an individual to Responses are generated by reassembly rules associated with operate a full seale computer from a remotely located type- selected decomposition rules. The fundamental technical prob- writer. The individual operator has the illusion thai, he is 75~.7c_'-5 lems with which ELIZA is concerned are: (1) the identification of the sole riser of the computer complex, while in facl~ others } :~:<:.. key words, (2) the discovery of minimal context, (3) the choice may be "time-sharing" the system with him. What is of appropriate transformations, (4) generation of responses in important here is that the computer can read messages }: the absence of key words, and (5) the provision of an editing typed on the typewriter and respond by writing oil the capability for ELIZA "scripts". A discussion of some psychologi- same instrument. %'he time between the computer's -.5~::a cal issues relevant to the ELIZA approach as well as of future receipt of a message and the appearance of its response is developments concludes the paper. a function of the program controlling the dialogue and of Introduction such MAC system parmneters as the number of users currently eon'esponding with the system. These latter It is said that• to explain is to explain away. This maxim parameters generally contribute so little to the overall is nowhere so well fulfilled as in the area of computer response time that conversational interaction with the programming, especially in what is ealled heuristic pro- computer need never involve truly intolerable delays. gramming and artifieiM intelligence. For in those realms :: L 2: .: When in conversation with ELIZA, tile user types in .i: machines are made to behave in wondrous ways, often some statement or set of statements in natm'al language suftieient to dazzle even the most experim~eed observer. using normal punetua.tion and sentence structures. Only i. :::! 7: But once a particular program is unmasked, once its the question mark may not be used, because it is inter- i );4pyL> inner workings are explained in language sufficiently plain preted as a line delete character by the MAC system. The to induce understanding, its magic crumbles away; iL user's sratement is terminated by a double carriage return st~mds revealed as a mere collection of procedures, each which serves to turn eontrol over to ELIZA. ELIZA Ithen >>7- quite comprehensible. The observer says to himself "I analyzes the user's statement and generates some response could have written that". With that thought he moves the whieh it types out.. Control is then again with the user. ::{ ) :2>J2 program in question from the shelf m~trked "intelligent", A ltypieal conversation is the following: to that reserved for curios, fit to be discussed only with Men are all alike. % people less enlightened than he. IN WHAT WAY They're always bugging us about something or other. Work reported herein was supported (iu prot) by Project MAC, CAN Y()U THINK (H: A SPECIFIC EXAMPLE i::i ::7 an _\-lIT research program sponsored by the Advm~ced Research Well, my boyfriend made me come here. Pr,,jects Aget,cy, l)~l)ar~met~t ~,1" l)ofense, under Office of Naval YOUR BOYFRIEND MAI)E YOU COME HERE ::.73:G{ ::::,• )i : Research Contract Number Nora'-4102(01). tie says i'm depressed much of the time. i:-(-: * Department of Eleeirieal Engineering. [ AM SORRY TO HEAR YOU ARE DEPRESSED 36 Comnutnieations of the .~(',M %olume 9 / Number / / January., 1966 2.: it'~ ~=~e. !. ant tmhappy. occurring in the input message. i)() ~ 0U TitlNK COMING IIERE WILl, IiELP YOU NOT TO (2) Tile identification of some minimal context within t@; iTNiIAPPY which the chosen keyword at)pears; e.g., if the keyword is i >cod some help, tidal m,,teh seems certain. "G'I~AT WOL'I,D IT MEAN TO YOU IF YOU GOT SOME IIELP "you", is it followed by the word "are" (in which ease an l'c, ri~ ps I could learn ~o get ahmgv, ith my mother. assertion is probably being made). 2-.f::LL 2~ii:: MORE ABOUT YOUE FAMILY (3) The choice of an appropriate transformation rule ),[5" -mnher takes care of me, and, of course, the making of the transformation itself. WiI() EI,SE IN ¥0UR FAMILY TAKES CAiIE 0F YOU (4) The provision of mechanism that will permit ),iy father. YO[/R FATHER ELIZA to respond "intelligently" when the input text 5-,)u are like my father in some ways. contained no keywords. ~t such a WiIAT RESEMBLANCE DO YOU SEE (5) The provision of machinery that facilitates editing, )lained . i. You are not vet',," aggressive but 1 think you don't wa.t~.t me to particularly extension, of the script on the script writing notice that. level. WHAT MAKES YOU TttINK I AM NOT VER~ AGGRESSIVE ~'ou dolt'; argue with me. There are, of course, the usual constraints dictated by the need to be eeononfical in the use of computer time and tral langu WIlY 1)O YOU THINK I DON'T ARGUE WITH YOU "~-(}u are afraid of me, storage space. ~resent, inn: DOES iT PLEASE YOU TO BEI, IE\'E I AM AFRA[I) OF YOU The central issue is clearly one of text manipulation, teal at _1[ My far her is afraid of everybody. and at the heart of that issue is the concept of the trans- ~94. Its n~ WHAT ELSE COMES TO MIND WtIEN YOU THINK OF formation rule which has been said to be associated with inereme~t:. Y()(-II FATHER certain keywords. The meehanisins subsumed under the ilities mat" Bullies. DOES THAT HA\-E ANYTtIING TO DO WITH THE FACT sloga.n "transformation rule" are a number of SLIP func- the Eli~e. TItAT YOUR BOYFR IENI) MADE YOU COME HERE tions which serve to (1) decompose a data string according tr even 1~: to certain criteria, hence to test the string as to whether it ity, howe; The capitalized lines are the machine responses. The gross procedure of the program is quite simple; the satisfies these criteria or not, and (2) to reassemble a decomposed string according to certain assembly specifica- ) cha.racte text: is read and inspected for the presence of a keyword. tions. individuai if such a word is found, the sentence is transformed While this is not the i)lace to discuss these functions in loeated t~ according to a rule associated with the keyword, if not a all their detail (or even to reveal their full power and ion that ii content-free renmrk or, under certain conditions, an earlier generality), it is important to the understanding of the in fact off: transformation is retrieved. The text so computed or operation of ELIZA to describe them in some detail. tint. Whai retrieved is then printed out. Consider the sentence "I ant very unhappy these days". ead messy;: In detail, of course, the procedure sketched above is Suppose a foreigner with only a limited knowledge of "riting 01i considerably more complex. Keywords, for example, amy English but with a veer good ear heard that sentence compute have a RAXK or precedence number. The procedure is spoken but understood only the first two words "I am". ts resp0i~ sensitive to such numbers in that it will abandon a key- Wishing to appear interested, perhaps even sympathetic, alogue and: word a.lready found in the left-to-right scan of the text in he may reply "How long have you been very unhappy ~ber of us fxvor of one having a higher rank. Also, the procedure these days?" What he nmst have done is to apply a kind These [~i~ reeo~,afizes a comma or a period as a delimiter. Whenever of template to the original sentence, one part of which o the 0vei either one is encountered and a keyword has already been matched the two words "I aln" and the remainder isolated ion with found, all snbsequent text is deleted from the input mes- the words "very unhat)py these days". He must also have .e delays. sage. If no key had yet been found the phrase or sentence a reassembly kit specifically associated with that template, user types to the left• of the delimiter (as well as the delimiter itself) one that specifies that any sentence of the form "I am ural lunge is deleted.