SUO: Re: Ontology
Jay,
I scanned the last few pages of Hilary Putnam's article
(copy below). In the opening pages, which I did not scan.
Putnam said that he had believed the received view that
Frege invented modern predicate calculus, which Russell
learned from Frege and that Russell occupied a central
position in the development of modern logic.
But as you can see, when Putnam read the original sources,
he made a surprising discovery: the received view on the
history of logic was completely wrong. The summary I gave
you was partly based on my own reading and partly based on
points I read in Putnam.
And please note the following paragraph by Putnam:
> The example of Loewenheim shows something else: metamathematical
> work (of a certain kind) did not have to wait for Russell and
> Whitehead to make Frege's work known (and to extend it and repair
> it). First-order logic (and its metamathematical study) would have
> existed without Frege. (Zermelo even denied that his set-theoretic
> work depended on Whitehead and Russell; he claimed to have been
> aware of the "Russell paradox" on his own.)
That's just what I said: If Frege and Russell had not existed,
the development of logic in Continental Europe would not have
been hindered at all. Putnam didn't mention the model-theoretic
issues, but as I said, if logicians had paid more attention to
Peirce's work, model theory would have been developed at least
20 years earlier.
John
________________________________________________________________
Peirce the Logician
by Hilary Putnam
Following is an excerpt of the last 5 pages of the article, which
was originally published in _Historia Mathematica_, vol. 9, 1982,
pp. 290-301. It was reprinted in H. Putnam, _Realism with a Human
Face_, Harvard University Press, 1990, pp. 252-260.
When I started to trace the later development of logic, the first
thing I did was to look at Schroeder's _Vorlesungen ueber die Algebra
der Logik_. This book, which appeared in three volumes, has a third
volume on the logic of relations (_Algebra und Logik der Relative_,
1895). The three volumes were the best-known logic text in the world
among advanced students, and they can safely be taken to represent
what any mathematician interested in the study of logic would have
had to know, or at least become acquainted with in the 1890s.
As the title suggests, the approach was algebraic (Boole's logic, as
we saw, grew out of abstract algebra), and the great problem was to
develop a logic of Relative (that is, relations). (The influence of the
German word Relativ is, perhaps, the reason Peirce always wrote "rel-
atives" and not "relations.") Peirce, although himself a member of the
algebraic school (he criticized himself for this in his correspondence),
had reservations about Schroeder's close assimilation of logical
problems to algebraic ones. "While I am not at all disposed to deny
that the so called 'solution problems', consisting in the ascertainment
of the general forms of relatives which satisfy given conditions, are
often of considerable importance, I cannot admit that the interest of
logical study centers in them," Peirce wrote. And "Since Professor
Schroeder carries his algebraicity so very far, and talks of 'roots',
'values', 'solutions', etc., when, even in my opinion, with my bias
towards algebra, such phrases are out of place..." But my purpose in
consulting this reference work was narrower; I simply wished to see how
Schroeder presented the quantifier.
Well, Schroeder does mention Frege's discovery, though just barely;
but he does not explain Frege's notation at all. The notation he both
explains and adopts (with credit to Peirce and his students, 0. H.
Mitchell and Christine Ladd-Franklin) is Peirce's. And this is no
accident: Frege's notation (like one of Peirce's schemes, the system of
existential graphs) repelled everyone (although Whitehead and Russell
were to study it with consequential results). Peirce's notation, in
contrast, was a typographical variant of the notation we use today. Like
modern notation, it lends itself to writing formulas on a line (Frege's
notation is two-dimensional) and to a simple analysis of normal-form
formulas into a prefix (which Peirce calls the Quantifier) and a matrix
(which Peirce calls the "Boolean part" of the formula).
Moreover, as Warren Goldfarb has emphasized in a fine paper on the
history of the quantifier, the Boolean school, including Peirce, was
willing to apply logical formulas to different "universes of discourse,"
and Peirce was willing (unlike Frege) to treat first-order logic
by itself, and not just as part of an ideal language (with a fixed
universe of discourse, namely, "all objects," for Frege). In fact --
and this may be surprising to others as it was to me -- the term
"first-order logic" is due to Peirce! (It has nothing to do with either
Russell's theory of types or Russell's theory of orders, although the
way Peirce distinguished between first-order and second-order formulas
-- by whether the "relative" is quantified over or not -- obviously has
something to do with logical type.) In summary, Frege tried to "sell"
a grand logical-metaphysical scheme with a dubious ontology, while
Peirce (and, following him, Schroeder) was busy "selling" a modest,
flexible, and extremely useful notation.
The success they experienced was impressive. While, to my knowledge,
no one except Frege ever published a single paper in Frege's
notation, many famous logicians adopted Peirce-Schroeder notation,
and famous results and systems were published in it. Loewenheim stated
and proved the Loewenheim theorem (later reproved and strengthened
by Skolem, whose name became attached to it together with Loewenheim's)
in Peircian notation. In fact, there is no reference in Loewenheim's
paper to any logic other than Peirce's. To cite another example,
Zermelo presented his axioms for set theory in Peirce-Schroeder
notation, and not, as one might have expected, in Russell-Whitehead
notation.
One can sum up these simple facts (which anyone can quickly verify)
as follows: Frege certainly discovered the quantifier first (four
years before 0. H. Mitchell, going by publication dates, which are
all we have as far as I know). But Leif Erikson probably discovered
America "first" (forgive me for not counting the native Americans,
who of course really discovered it "first"). If the effective
discoverer, from a European point of view, is Christopher Columbus,
that is because he discovered it so that it stayed discovered (by
Europeans, that is), so that the discovery became known (by Europeans).
Frege did "discover" the quantifier in the sense of having the rightful
claim to priority; but Peirce and his students discovered it in the
effective sense. The fact is that until Russell appreciated what he had
done, Frege was relatively obscure, and it was Peirce who seems to have
been known to the entire world logical community. How many of the
people who think that "Frege invented logic" are aware of these facts?
The example of Loewenheim shows something else: metamathematical
work (of a certain kind) did not have to wait for Russell and
Whitehead to make Frege's work known (and to extend it and repair
it). First-order logic (and its metamathematical study) would have
existed without Frege. (Zermelo even denied that his set-theoretic
work depended on Whitehead and Russell; he claimed to have been
aware of the "Russell paradox" on his own.)
The Peircian Influence on Whitehead and Russell
Still, I thought, Russell and Whitehead themselves certainly learned
their logic from Frege. To check this I turned to Russell's autobio-
graphical writings. The result was frustrating. In _My Philosophical
Development_, Russell describes the impact that meeting Peano had
upon his logical development. Strangely enough, he does not mention
the quantifier, which seems so very central from our present point of
view, at all. Peano taught Russell what was a commonplace in the
Peirce-Schroeder logical community, the difference in logical form
between all men are mortal and Socrates is a man. And it is clear that
one of the notations used in Principia for a universally quantified
conditional -- writing the variable of quantification under the sign of
the conditional -- came from Peano. But the quantifier as such is not
something that Russell singled out for discussion (unless there is
something in the unpublished Nachiass in the Russell Archives in
Ontario). Even when Russell discusses his debt to Frege (in a peculiar
way: Russell is unstinting in his praise of Frege's genius, but claims
to have thought of the definition of number quite independently), he
does not mention the quantifier. Principia is no more help on this
score, although there is an indication in it that most of the specific
notations were invented by Whitehead rather than Russell.
[Footnote: Subsequent to writing this essay I discovered that, in
"Whitehead and Principia Mathematica," Mind (1948), p. 137, Russell says
that Whitehead contributed the notion for the universal quantifier.]
Since I have mentioned Peano, I should remark that he was not only
well acquainted with Peirce-Schroeder logic, but he had actually
corresponded with Peirce.
In desperation, I looked at Whitehead's _Universal Algebra_. This is
a work squarely in the tradition to which Boole, Schroeder, and Peirce
belonged, the tradition that treated general algebra and logic as vir-
tually one subject. And here, before Whitehead worked with Russell,
there is no mention of Frege, but there is a citation of "suggestive
papers" by Peirce's students 0. H. Mitchell and Christine Ladd-
Franklin.15 The topic, of course, is the quantifier.
In sum, Whitehead certainly caine to his knowledge of quantification
through "Peirce and his students." On the other hand, the axioms
in Principia are almost certainly derived from Frege's Begriffsschrift;
Pcirce gave no system of axioms for first-order logic, although his
existential graphs" are a complete proof procedure for first-order
bigic (an early form of natural deduction).
I have, if anything, minimized Frege's contribution and played up the
Boolean contribution for reasons which I have explained. But to leave
matters here would be as unjust to Frege and to a third tradition, the
Hilbert tradition (proof theory), as Quine's unfortunate remark was
to the Boolean tradition.
Frege's work is sometimes disparaged today (I mean Frege's logical
achievement; Frege's stock as a philosopher has never been higher),
tough not, of course, by Quine. It is conceded that Frege was far
tore rigorous and, in particular, far more consistently free of use-
mention confusions than other logicians; but such domestic virtue is
no longer felt to be impressive. The central charge laid against his
work (and that of Whitehead and Russell) is that what they called
logic is not logic but "set theory," and that reducing arithmetic
to set theory is a bad idea.
This raises philosophical issues far too broad for this essay. But
let me just make two comments on this: (1) Where to draw the line
between logic and set theory (or predicate theory) is not an easy
question. The statement that a syllogism is valid, for example, is a
statement of second-order logic. (Barbara is valid just in case
(F)(G)(H)((Fx => Gx) & (Gx => Hx) => (Fx => Hx)),
for example.) If second-order logic is "set theory," then most of
traditional logic thus becomes set theory." (2) The full intuitive
principle of mathematical induction is definitely second-order in
anybody's view. Thus there is a higher-order element in arithmetic
whether or not one chooses to "identify numbers with sets" (just
as Frege realized).
But, philosophical questions aside, Frege certainly undertook one
of the most ambitious logical investigations in all history. Its
enormous sweep made it (after its repair by Whitehead and Russell, and
its translation into a notation resembling Peirce's) a great stimulus to
all future work in the field. The Hilbert school certainly put it in the
center of their proof theoretic investigations: Goedel's most famous
paper, after all, bears the title "On Principia Mathematica and Related
Systems," That all its achievements could he imitated successfully by
the Cantorians (Zermelo and von Neumann) does not take away either
its priority or its influence. If Peirce and Schroeder were the
cutting edge of the logical world prior to Russell and Whitehead's
Principia Mathematica (or a cutting edge -- the Hilbert school was
already under way), after the appearance of Principia their work lost
its importance -- or lost it except for one important thing: its
influence on Hilbert, who followed Peirce in separating off first-order
logic from the higher system for metamathematical study.
Principia in turn was to lose its cutting-edge position when interest
shifted from the construction of systems (and the derivation of
mathematics within them) to the metamathematical study of properties of
systems. Nothing remains forever the cutting edge in a healthy science.
But a fair-minded statement of the historical importance of the
different schools of work, a statement that does justice to each
without slighting the others, should not be impossible. Such a statement
was given by Hilbert and Ackermann:
The first clear idea of a mathematical logic was formulated by
Leibniz. The first results were obtained by A. de Morgan (1806 --
1876) and G. Boole (1815 -- 1864). The entire later development goes
back to Boole. Among his successors, W. S. Jevons (1835 -- 1882) and
especially C. S. Peirce (1839 -- 1914) enriched the young science.
Ernst Schroeder systematically organized and supplemented the
various results of his predecessors in his _Vorlesungen ueber die
Algebra der Logik_ (1890 -- 1895), which represents a certain
completion of the series of developments proceeding from Boole.
In part independently of the development of the Boole-Schroeder
algebra, symbolic logic received a new impetus from the need of
mathematics for an exact foundation and strict axiomatic treatment.
G. Frege published his Begriffsschrift in 1879 and his Grundgesetze
der Arithmetik in 1893 -- 1903. G. Peano and his co-workers began
in 1894 the publication of the Formulaire des Mathematiques, in
which all the mathematical disciplines were to be presented in terms
of the logical calculus. A high point of this development is the
appearance of the Principia Mathematica (1910 -- 1913) by A. N.
Whitehead and B. Russell. Most recently Hilbert, in a series of
papers and university lectures, has used the logical calculus to
find a new way of building up mathematics which makes it possible
to recognize the consistency of the postulates adopted. The first
comprehensive account of these researches has appeared in the
_Grundlagen der Mathematik_ (1934 1939), by D. Hilbert and
P. Bernays.
If Quine had produced a statement like this in his book, I should not
have had a topic for this essay!