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Reportedly, Alan Kay is the inventor of the term "object oriented". And he is often quoted as having said that what we call OO today is not what he meant.

For example, I just found this on Google:

I made up the term 'object-oriented', and I can tell you I didn't have C++ in mind

-- Alan Kay, OOPSLA '97

I vaguely remember hearing something pretty insightful about what he did mean. Something along the lines of "message passing".

Do you know what he meant? Can you fill in more details of what he meant and how it differs from today's common OO? Please share some references if you have any.


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C++ is starting to be a taboo language. –  jokoon Feb 11 '11 at 13:06
Having seen (and used) all three, I'd say C++ is a lot closer than Smalltalk to what Ole Johann Dahl and Kristen Nygaard had in mind when they invented object oriented programming itself. Looked at in context (in 1997 C++ seemed to be taking over all of programming, and Smalltalk was all but dead) it mostly meant that Alan Kay was a sore loser. –  Jerry Coffin Feb 11 '11 at 16:35
@Jerry Coffin: There are more JavaScript than Haskell programmers. Does that make JavaScript the reference for functional programming? –  back2dos Mar 16 '11 at 19:15
@back2dos: Simple: it's pretty clearly what motivated him to make a statement that, from an objective (no pun intended) viewpoint was a simple falsehood: C++ clearly did (and still does) include the features that Alan Kay (along with many others) had agreed were necessary for object oriented programming. –  Jerry Coffin Mar 16 '11 at 22:46
@back2dos: Nonsense. Alan Kay knew that message passing is simply a way of implementing polymorphism. Claiming that the mechanism matters is basically repudiating OOP as a whole. We're left with two possible conclusions: Alan Kay was a marketroid who devised a nice term, but was clueless about what it meant, or he was a sore loser who said nasty things about the language that beat out the one he preferred, and then came up with a weak, nonsensical excuse. His other writing is sufficient to eliminate the possibility of ignorant marketroid, leaving only "sore loser." –  Jerry Coffin Mar 17 '11 at 13:57

3 Answers 3

Most if not all of what Alan Kay meant by object-orientation is embodied in the Smalltalk language.

"We didn’t even do all of the idea at PARC. Many of Carl Hewitt’s Actors ideas which got sparked by the original Smalltalk were more in the spirit of OOP than the subsequent Smalltalks. Significant parts of Erlang are more like a real OOP language the the current Smalltalk, and certainly the C based languages that have been painted with “OOP paint”."

Taken from Alan Kay's comment at:


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Date: Wed, 23 Jul 2003 09:33:31 -0800
To: Stefan Ram [removed for privacy]
From: Alan Kay [removed for privacy]
Subject: Re: Clarification of "object-oriented"

Hi Stefan --

Sorry for the delay but I was on vacation.

At 6:27 PM +0200 7/17/03, Stefan Ram wrote:

Dear Dr. Kay,

I would like to have some authoritative word on the term "object-oriented programming" for my tutorial page on the subject. The only two sources I consider to be "authoritative" are the International Standards Organization, which defines "object-oriented" in "ISO/IEC 2382-15", and you, because, as they say, you have coined that term.

I'm pretty sure I did.

Unfortunately, it is difficult to find a web page or source with your definition or description of that term. There are several reports about what you might have said in this regard (like "inheritance, polymorphism and encapsulation"), but these are not first-hand sources. I am also aware that later you put more emphasis on "messaging" - but I still would like to know about "object oriented".

For the records, my tutorial page, and further distribution and publication could you please explain:

When and where was the term "object-oriented" used first?

At Utah sometime after Nov 66 when, influenced by Sketchpad, Simula, the design for the ARPAnet, the Burroughs B5000, and my background in Biology and Mathematics, I thought of an architecture for programming. It was probably in 1967 when someone asked me what I was doing, and I said: "It's object-oriented programming".

The original conception of it had the following parts.

  • I thought of objects being like biological cells and/or individual computers on a network, only able to communicate with messages (so messaging came at the very beginning -- it took a while to see how to do messaging in a programming language efficiently enough to be useful).

  • I wanted to get rid of data. The B5000 almost did this via its almost unbelievable HW architecture. I realized that the cell/whole-computer metaphor would get rid of data, and that "<-" would be just another message token (it took me quite a while to think this out because I really thought of all these symbols as names for functions and procedures.

  • My math background made me realize that each object could have several algebras associated with it, and there could be families of these, and that these would be very very useful. The term "polymorphism" was imposed much later (I think by Peter Wegner) and it isn't quite valid, since it really comes from the nomenclature of functions, and I wanted quite a bit more than functions. I made up a term "genericity" for dealing with generic behaviors in a quasi-algebraic form.

  • I didn't like the way Simula I or Simula 67 did inheritance (though I thought Nygaard and Dahl were just tremendous thinkers and designers). So I decided to leave out inheritance as a built-in feature until I understood it better.

My original experiments with this architecture were done using a model I adapted from van Wijngaarten's and Wirth's "Generalization of Algol" and Wirth's Euler. Both of these were rather LISP-like but with a more conventional readable syntax. I didn't understand the monster LISP idea of tangible metalanguage then, but got kind of close with ideas about extensible languages draw from various sources, including Irons' IMP.

The second phase of this was to finally understand LISP and then using this understanding to make much nicer and smaller and more powerful and more late bound understructures. Dave Fisher's thesis was done in "McCarthy" style and his ideas about extensible control structures were very helpful. Another big influence at this time was Carl Hewitt's PLANNER (which has never gotten the recognition it deserves, given how well and how earlier it was able to anticipate Prolog).

The original Smalltalk at Xerox PARC came out of the above. The subsequent Smalltalk's are complained about in the end of the History chapter: they backslid towards Simula and did not replace the extension mechanisms with safer ones that were anywhere near as useful.

What does "object-oriented [programming]" mean to you? (No tutorial-like introduction is needed, just a short explanation [like "programming with inheritance, polymorphism and encapsulation"] in terms of other concepts for a reader familiar with them, if possible. Also, it is not neccessary to explain "object", because I already have sources with your explanation of "object" from "Early History of Smalltalk".)

(I'm not against types, but I don't know of any type systems that aren't a complete pain, so I still like dynamic typing.)

OOP to me means only messaging, local retention and protection and hiding of state-process, and extreme late-binding of all things. It can be done in Smalltalk and in LISP. There are possibly other systems in which this is possible, but I'm not aware of them.

[Also,] One of the things I should have mentioned is that there were two main paths that were catalysed by Simula. The early one (just by accident) was the bio/net non-data-procedure route that I took. The other one, which came a little later as an object of study was abstract data types, and this got much more play.

If we look at the whole history, we see that the proto-OOP stuff started with ADT, had a little fork towards what I called "objects" -- that led to Smalltalk, etc.,-- but after the little fork, the CS establishment pretty much did ADT and wanted to stick with the data-procedure paradigm. Historically, it's worth looking at the USAF Burroughs 220 file system (that I described in the Smalltalk history), the early work of Doug Ross at MIT (AED and earlier) in which he advocated embedding procedure pointers in data structures, Sketchpad (which had full polymorphism -- where e.g. the same offset in its data structure meant "display" and there would be a pointer to the appropriate routine for the type of object that structure represented, etc., and the Burroughs B5000, whose program reference tables were true "big objects" and contained pointers to both "data" and "procedures" but could often do the right thing if it was trying to go after data and found a procedure pointer. And the very first problems I solved with my early Utah stuff was the "disappearing of data" using only methods and objects. At the end of the 60s (I think) Bob Balzer wrote a pretty nifty paper called "Dataless Programming", and shortly thereafter John Reynolds wrote an equally nifty paper "Gedanken" (in 1970 I think) in which he showed that using the lamda expressions the right way would allow data to be abstracted by procedures.

The people who liked objects as non-data were smaller in number, and included myself, Carl Hewitt, Dave Reed and a few others -- pretty much all of this group were from the ARPA community and were involved in one way or another with the design of ARPAnet → Internet in which the basic unit of computation was a whole computer. But just to show how stubbornly an idea can hang on, all through the seventies and eighties, there were many people who tried to get by with "Remote Procedure Call" instead of thinking about objects and messages. Sic transit gloria mundi.


Alan Kay

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HTTP/1.1 403 Access Denied. –  Job Mar 16 '11 at 18:01
I was just able to access it, so it must have been a transient problem. Thanks for that link, Manoj. –  David Conrad Mar 24 '11 at 13:36
That's a great link. Thanks. –  Charlie Flowers Jun 23 '11 at 3:53
@Job Wednesday (March 16th, the day you apparently got the 403 error) is the monthly service day of the domain admin at userpage.fu-berlin.de). They routinely take parts of the network offline once a month. Uh, yeah, don’t ask … –  Konrad Rudolph Jul 8 '11 at 11:45

Most if not all of what Alan Kay meant by object-orientation is embodied in the Smalltalk language.

Also, from http://en.wikipedia.org/wiki/Message_passing#Influences_on_other_programming_models:

Alan Kay has argued that message passing is more important than objects in OOP, and that objects themselves are often over-emphasized. The live distributed objects programming model builds upon this observation; it uses the concept of a distributed data flow to characterize the behavior of a complex distributed system in terms of message patterns, using high-level, functional-style specifications.
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One then wonders why he called it "Object-Oriented" rather than "Message-Oriented". –  David Thornley Mar 16 '11 at 17:36
@David Thornley: So that would make C++ method-oriented? –  back2dos Mar 16 '11 at 19:12
I was too blythe about the term back in the 60s and should have chosen something like "message oriented" –  Alan Kay Jun 8 '11 at 16:27
@Alan Kay - Thank you for your comment. So that sort of confirms for me that to you, message passing is one of the most foundational concepts. And to me, that emphasizes late binding, duck typing, behavior-oriented design (as in "tell don't ask"), etc. Am I in the right ballpark? –  Charlie Flowers Jun 23 '11 at 3:47
But what is "message oriented" then? (I can think of async calls (possibly), but don't actually know any language not implementing more-or-less "normal" methods; there's a thing about return values, also, but this can be tricked with sort-of 'ref'/'out' parameters or something like that) –  mlvljr Jul 6 '11 at 22:49

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