The artefact, talking
The demonstration dialogue
This is the conversation Terry Winograd published as the demonstration of SHRDLU, reproduced verbatim from his own transcript. The person types in lower case; SHRDLU answers in capitals. The original typographical quirks are preserved, including the misspelling "ANWHERE" and the irregular spacing, because they are evidence of the transcript's status as a hand-written artefact, which is part of what a critical reading looks at as a paratext related to the source code, part of the historical contextualisation of critical code studies.
begin
1 Personpick up a big red block.
SHRDLUOK. (does it)
2 Persongrasp the pyramid.
SHRDLUI DON'T UNDERSTAND WHICH PYRAMID YOU MEAN.
3 Personfind a block which is taller than the one you are holding and put it into the box.
SHRDLUBY "IT", I ASSUME YOU MEAN THE BLOCK WHICH IS TALLER THAN THE ONE I AM HOLDING.
OK. (does it)
4 Personwhat does the box contain?
SHRDLUTHE BLUE PYRAMID AND THE BLUE BLOCK.
5 Personwhat is the pyramid supported by?
SHRDLUTHE BOX.
6 Personhow many blocks are not in the box?
SHRDLUFOUR OF THEM.
7 Personis at least one of them narrower than the one which I told you to pick up?
SHRDLUYES, THE RED CUBE.
SHRDLUYES, BY THE TABLE.
9 Personcan the table pick up blocks?
SHRDLUNO.
10 Personcan a pyramid be supported by a block?
SHRDLUYES.
11 Personcan a pyramid support a pyramid?
SHRDLUI DON'T KNOW.
12 Personstack up two pyramids.
SHRDLUI CAN'T.
13 Personwill you please stack up both of the red blocks and either a green cube or a pyramid?
SHRDLUOK. (does it)
14 Personwhich cube is sitting on the table?
SHRDLUTHE LARGE GREEN ONE WHICH SUPPORTS THE RED PYRAMID.
15 Personis there a large block behind a pyramid?
SHRDLUYES, THREE OF THEM: A LARGE RED ONE, A LARGE GREEN CUBE, AND THE BLUE ONE.
16 Personput a small one onto the green cube which supports a pyramid.
SHRDLUOK. (does it)
17 Personput the littlest pyramid on top of it.
SHRDLUOK. (does it)
18 Persondoes the shortest thing the tallest pyramid's support supports support anything green?
SHRDLUYES, THE GREEN PYRAMID.
19 Personwhat color is it?
SHRDLUBY "IT", I ASSUME YOU MEAN THE SHORTEST THING THE TALLEST PYRAMID'S SUPPORT SUPPORTS.
RED
20 Personhow many things are on top of green cubes?
SHRDLUI'M NOT SURE WHAT YOU MEAN BY "ON TOP OF" IN THE PHRASE "ON TOP OF GREEN CUBES".
DO YOU MEAN:
1 - DIRECTLY ON THE SURFACE
2 - ANWHERE ON TOP OF ?
Person2
SHRDLUTHREE OF THEM.
21 Personhad you touched any pyramid before you put the green one on the little cube?
SHRDLUYES, THE GREEN ONE.
22 Personwhen did you pick it up?
SHRDLUWHILE I WAS STACKING UP THE RED CUBE, A LARGE RED BLOCK AND A LARGE GREEN CUBE.
SHRDLUTO GET RID OF IT.
24 Personwhy did you do that?
SHRDLUTO CLEAN OFF THE RED CUBE.
25 Personwhy did you clear off that cube?
SHRDLUTO PUT IT ON A LARGE GREEN CUBE.
26 Personwhy did you do that?
SHRDLUTO STACK UP THE RED CUBE, A LARGE RED BLOCK AND A LARGE GREEN CUBE.
27 Personwhy did you do that?
SHRDLUBECAUSE YOU ASKED ME TO.
28 Personhow did you do it?
SHRDLUBY PUTTING A LARGE RED BLOCK ON THE TABLE; THEN LETTING GO OF IT; THEN PUTTING A LARGE GREEN CUBE ON IT; THEN LETTING GO OF THAT CUBE; THEN PUTTING THE RED CUBE ON THAT CUBE; THEN LETTING GO OF THAT CUBE.
29 Personhow many objects did you touch while you were doing it?
SHRDLUFOUR OF THEM.
30 Personwhat did the red cube support before you started to clean it off?
SHRDLUTHE GREEN PYRAMID.
31 Personthere were five blocks to the left of the box then.
SHRDLUNO, ONLY FOUR OF THEM: THE RED CUBE, TWO LARGE GREEN CUBES AND A LARGE RED BLOCK.
32 Personput the blue pyramid on the block in the box.
SHRDLUOK. (does it)
33 Personis there anything which is bigger than every pyramid but is not as wide as the thing that supports it?
SHRDLUYES, THE BLUE BLOCK.
SHRDLU(interrupting) SORRY, I DON'T KNOW THE WORD "STEEPLE".
35 Persona "steeple" is a stack which contains two green cubes and a pyramid.
SHRDLUI UNDERSTAND.
36 Personare there any steeples now?
SHRDLUNO.
SHRDLUOK. (does it)
38 Personcall the biggest block "superblock".
SHRDLUOK.
39 Personhave you picked superblock up since we began?
SHRDLUYES.
40 Personwhy did you drop it?
SHRDLUBY "IT", I ASSUME YOU MEAN THE SUPERBLOCK.
I CAN'T EXPLAIN A NON-EXISTENT EVENT.
41 Personis there anything to the right of the red pyramid?
SHRDLUYES, FOUR THINGS: THE BOX, THE RED CUBE, THE BLUE PYRAMID AND THE BLOCK NAMED SUPERBLOCK.
SHRDLUYOU'RE WELCOME!
Source: Terry Winograd, "The dialog that was used as a SHRDLU demo", hci.stanford.edu/winograd/shrdlu (archived). Reproduced verbatim, typos and spacing preserved.
reading the conversation
Commentary
What the dialogue is doing
Read as a text, the conversation is a carefully ordered argument for machine understanding. Each exchange exhibits a distinct capacity.
Reference and ambiguity
"Grasp the pyramid" is met not with an action but with a question: I DON'T UNDERSTAND WHICH PYRAMID YOU MEAN. SHRDLU knows there is more than one pyramid and that the definite article presupposes a unique referent. A few lines later it resolves "it" by spelling out the description it has inferred, "BY 'IT', I ASSUME YOU MEAN…". This is anaphora and presupposition handled in context, the very phenomena that the later Winograd Schema Challenge would make a benchmark.
A model of the world, queried
"What does the box contain?", "what is the pyramid supported by?", "how many blocks are not in the box?" treat the blocks world as a small database of spatial relations. SHRDLU is not pattern-matching on the words; it is consulting a model and computing. "CAN THE TABLE PICK UP BLOCKS? NO." and "CAN A PYRAMID SUPPORT A PYRAMID? I DON'T KNOW." show the difference between what the world rules out and what the program simply has no axiom for. The reply "I DON'T KNOW" is interesting for showing the limits of the expert system's knowledge base.
The goal stack speaks
The chain of "why?" questions is the most quoted passage, and the most revealing. "TO GET RID OF IT", "TO CLEAN OFF THE RED CUBE", up to "BECAUSE YOU ASKED ME TO", is SHRDLU reading back its own Micro-Planner goal stack. The machine can explain itself because its reasoning was an explicit structure of goals and sub-goals. This readability is precisely what today's neural systems lack, and it is worth holding onto as a design value even as we read the demo sceptically.
Learning, and refusing
Near the end the person defines a new word, "a 'steeple' is a stack which contains two green cubes and a pyramid", and SHRDLU answers "I UNDERSTAND" and can then build one. It also refuses gracefully: asked why it dropped the superblock, it corrects the false presupposition, "I CAN'T EXPLAIN A NON-EXISTENT EVENT."
The seam in the artefact
The misspelling "ANWHERE" and the irregular spacing are small but telling. This is a prepared transcript, the dialogue Winograd himself later described as "very carefully worked through, line by line." The conversation is real in that SHRDLU could produce these responses, but staged in that the path through them was chosen in advance. This is important to note for a critical reading as the dialogue is a demonstration, a synthetic artefact to support the descriptions of the system's capacities. Was this a 'con' in the sense that Weizenbaum would have described it? That would depend on whether scripted evidence is used to further funding requests or whether it was described as such. This is one of the interesting lines of questioning we will explore, and reminds one of the boosterism we see in the partial examples shown by the frontier model AI companies today.
