# Frasi di Georg Cantor

## Georg Cantor

**Data di nascita:** 3. Marzo 1845**Data di morte:** 6. Gennaio 1918

Georg Ferdinand Ludwig Philipp Cantor è stato un matematico tedesco, padre della moderna teoria degli insiemi. Cantor ha allargato la teoria degli insiemi fino a comprendere al suo interno i concetti di numeri transfiniti, numeri cardinali e ordinali.

### Autori simili

### Frasi Georg Cantor

### „L'essenza della matematica è la sua libertà.“

— Georg Cantor

in A. P. Hillman e G. L. Alexanderson, A First Undergraduate Course in Abstract Algebra, 1973

### „In particolare, nell'introdurre nuovi numeri, la matematica ha come unico obbligo quello di dare delle definizioni di essi, per mezzo delle quali verrà data una definibilità e, se le circostanze lo permettono, una relazione tale rispetto ai vecchi numeri che in certi casi potranno essere distinguibili senza dubbio dagli altri numeri. Ogniqualvolta un numero soddisfa tutte queste condizioni, esso può e deve essere considerato in matematica come esistente e reale. Questo è per me il motivo per cui bisogna considerare i numeri razionali, irrazionali e complessi pienamente esistenti, come gli interi positivi finiti.“

— Georg Cantor

in David Foster Wallace, Tutto e di più – storia compatta dell'∞, 2005

### „The transfinite numbers are in a certain sense themselves new irrationalities“

— Georg Cantor

Context: The transfinite numbers are in a certain sense themselves new irrationalities and in fact in my opinion the best method of defining the finite irrational numbers is wholly dissimilar to, and I might even say in principle the same as, my method described above of introducing transfinite numbers. One can say unconditionally: the transfinite numbers stand or fall with the finite irrational numbers; they are like each other in their innermost being; for the former like the latter are definite delimited forms or modifications of the actual infinite.
As quoted in Understanding the Infinite (1994) by Shaughan Lavine

### „The totality of all alephs cannot be conceived as a determinate, well-defined, and also a finished set.“

— Georg Cantor

Context: The totality of all alephs cannot be conceived as a determinate, well-defined, and also a finished set. This is the punctum saliens, and I venture to say that this completely certain theorem, provable rigorously from the definition of the totality of all alephs, is the most important and noblest theorem of set theory. One must only understand the expression "finished" correctly. I say of a set that it can be thought of as finished (and call such a set, if it contains infinitely many elements, "transfinite" or "suprafinite") if it is possible without contradiction (as can be done with finite sets) to think of all its elements as existing together, and to think of the set itself as a compounded thing for itself; or (in other words) if it is possible to imagine the set as actually existing with the totality of its elements.
Letter to David Hilbert (2 October 1897)

### „This view [of the infinite], which I consider to be the sole correct one, is held by only a few.“

— Georg Cantor

Context: This view [of the infinite], which I consider to be the sole correct one, is held by only a few. While possibly I am the very first in history to take this position so explicitly, with all of its logical consequences, I know for sure that I shall not be the last!
As quoted in Journey Through Genius (1990) by William Dunham ~

### „I call this the improper infinite“

— Georg Cantor

Context: As for the mathematical infinite, to the extent that it has found a justified application in science and contributed to its usefulness, it seems to me that it has hitherto appeared principally in the role of a variable quantity, which either grows beyond all bounds or diminishes to any desired minuteness, but always remains finite. I call this the improper infinite [das Uneigentlich-unendliche].

### „I have never proceeded from any Genus supremum of the actual infinite. Quite the contrary, I have rigorously proved that there is absolutely no Genus supremum of the actual infinite. What surpasses all that is finite and transfinite is no Genus; it is the single, completely individual unity in which everything is included, which includes the Absolute, incomprehensible to the human understanding. This is the Actus Purissimus, which by many is called God.“

— Georg Cantor

Context: I have never proceeded from any Genus supremum of the actual infinite. Quite the contrary, I have rigorously proved that there is absolutely no Genus supremum of the actual infinite. What surpasses all that is finite and transfinite is no Genus; it is the single, completely individual unity in which everything is included, which includes the Absolute, incomprehensible to the human understanding. This is the Actus Purissimus, which by many is called God.
I am so in favor of the actual infinite that instead of admitting that Nature abhors it, as is commonly said, I hold that Nature makes frequent use of it everywhere, in order to show more effectively the perfections of its Author. Thus I believe that there is no part of matter which is not — I do not say divisible — but actually divisible; and consequently the least particle ought to be considered as a world full of an infinity of different creatures.
As quoted in Out of the Mouths of Mathematicians : A Quotation Book for Philomaths (1993) by Rosemary Schmalz.

### „Mathematics is in its development entirely free and is only bound in the self-evident respect that its concepts must both be consistent with each other, and also stand in exact relationships, ordered by definitions, to those concepts which have previously been introduced and are already at hand and established.“

— Georg Cantor

Context: Mathematics is in its development entirely free and is only bound in the self-evident respect that its concepts must both be consistent with each other, and also stand in exact relationships, ordered by definitions, to those concepts which have previously been introduced and are already at hand and established. In particular, in the introduction of new numbers, it is only obligated to give definitions of them which will bestow such a determinacy and, in certain circumstances, such a relationship to the other numbers that they can in any given instance be precisely distinguished. As soon as a number satisfies all these conditions, it can and must be regarded in mathematics as existent and real.

### „My theory stands as firm as a rock; every arrow directed against it will return quickly to its archer.“

— Georg Cantor

Context: My theory stands as firm as a rock; every arrow directed against it will return quickly to its archer. How do I know this? Because I have studied it from all sides for many years; because I have examined all objections which have ever been made against the infinite numbers; and above all because I have followed its roots, so to speak, to the first infallible cause of all created things.
As quoted in Journey Through Genius (1990) by William Dunham

### „What I assert and believe to have demonstrated in this and earlier works is that following the finite there is a transfinite (which one could also call the supra-finite), that is an unbounded ascending ladder of definite modes, which by their nature are not finite but infinite, but which just like the finite can be determined by well-defined and distinguishable numbers.“

— Georg Cantor

As quoted in Understanding the Infinite (1994) by Shaughan Lavine ~

### „I entertain no doubts as to the truths of the transfinites, which I recognized with God’s help and which, in their diversity, I have studied for more than twenty years; every year, and almost every day brings me further in this science.“

— Georg Cantor

As quoted in Modern Mathematicians, (1995) by Harry Henderson. ~

### „The actual infinite arises in three contexts: first when it is realized in the most complete form, in a fully independent otherworldly being, in Deo, where I call it the Absolute Infinite or simply Absolute; second when it occurs in the contingent, created world; third when the mind grasps it in abstracto as a mathematical magnitude, number or order type.“

— Georg Cantor

As quoted in Mind Tools: The Five Levels of Mathematical Reality (1988) by Rudy Rucker. ~

### „Had Mittag-Leffler had his way, I should have to wait until the year 1984, which to me seemed too great a demand!“

— Georg Cantor

Letter (1885), written after Gösta Mittag-Leffler persuaded him to withdraw a submission to Mittag-Leffler's journal Acta Mathematica, telling him it was "about one hundred years too soon."