[Giordano Bruno's] fame is partly due to the tragedy of his life and death, but no less deserved by his brilliant gifts as a thinker and writer. His vision of the world has a distinctly modern quality, and has impressed and influenced scientists and philosophers throughout the subsequent centuries. At the same time, his work is still entirely a part of the Renaissance, not merely in its date and style but in its premises and problems, whereas such younger contemporaries or successors as Bacon, Galileo, and Descartes belong to the Renaissance with only a part, and perhaps not the most significant part, of their thought and work.

Giordano Bruno was born in Nola in southern Italy in 1548, and entered the Dominican order in Naples at the age of 18. While pursuing theological studies, he also read extensively in the ancient philosophers, and began to entertain serious doubts about some of the teachings of the Catholic Church. When he was in Rome in 1576, these doubts became known to the authorities of his order, and an indictment for heresy was prepared against him. Before he could be arrested, Bruno escaped and began a long and adventurous journey that took him to many parts of Europe. He went first to Noli near Genoa, then to Savona, Turin, Venice, and Padua, and apparently earned his living by private teaching and tutoring, as he did throughout most of his later life until his arrest. From Padua he went to Lyons, and then to Geneva, where he became a Calvinist and met many of the Reformed leaders. Yet soon he turned against Calvinism and went to Toulouse, where he obtained a degree in theology and lectured on Aristotle for two years. Next he went to Paris, where he obtained the favor of Henry III, held some kind of a lectureship, and published his first writings in 1582. He then accompanied the French ambassador, Michel de Castelnaud, Marquis de Mauvissière, to England, and spent the period from 1583 to 1585 in London. He also held a disputation, and gave a few lectures, at Oxford, and antagonized the professors both by his manners and by his polemical attacks. Yet he made friendly contact with Sir Philip Sidney and other educated Englishmen, and his English period is especially noteworthy because he published in London, in Italian, some of his most famous writings.

He returned to Paris with his patron, and held in 1586 in one of the colleges of the university a violent disputation against Aristotle, which caused such an uproar that he decided to leave. He went to Marburg and then to Wittenberg, where he lectured for two years at the university on Aristotle's logic, became a Lutheran, and praised Luther in his farewell address. He then proceeded to Prague and to Helmstedt, where he lectured again at the university, and in 1590 to Frankfurt. His stay in Frankfurt was again important, since it was in this city, which was then, as now, a center of the international book trade, that he published his Latin poems (1591), the most important of his published works after his Italian dialogues.

When he was in Frankfurt, he received and accepted an invitation from Giovanni Mocenigo, a Venetian nobleman. After a short stay in Padua, Bruno joined the household of Mocenigo in Venice as his guest and tutor. Shortly afterwards, Mocenigo denounced him to the Inquisition and had him arrested in 1592. Bruno tried to retract, but in January 1593 he was taken to Rome, kept in prison, and subjected to a trial that lasted for many years. After initial hesitations, he firmly refused to recant his philosophical opinions. Finally, in February 1600, he was sentenced to death and burned alive in the Campo di Fiori, where a monument was erected to him during the last century.

Bruno's dreadful end has rightly shocked his contemporaries and posterity. His firm conduct during the trial deserves our highest respect, and goes a long way to balance his human weaknesses, which are all too obvious. The idea that a man should be punished and executed for holding opinions considered wrong by his religious or political authorities is intolerable for any thoughtful person who takes human dignity and liberty seriously, although the deplorable treatment given to Bruno, and the wrong idea underlying it, was by no means peculiar to Bruno's church or to his century, as some historians would have us believe. His death made of Bruno a martyr, not so much of modern science, as was thought for a long time, but rather of his convictions and of philosophical liberty. The records of his trial have not been completely preserved, but several relevant documents have been published, and some very important ones have come to light quite recently, from which the nature and content of the charges made against him have become much clearer than before. It is now quite evident that Bruno's acceptance of the Copernican system constituted but one out of a very large number of accusations, which included a long series of philosophical and theological opinions as well as many specific instances of alleged blasphemy and violations of Church discipline.

Bruno's extant writings are rather numerous and diverse in content. His Italian works, which were all published during his lifetime, include a comedy and several satirical treatises, in addition to his philosophical dialogues, which we shall discuss later. His style is lively and exuberant, and at times quite baroque and obscure. His more numerous Latin writings, some of which were published only in the last century whereas others have come to light quite recently, include several important philosophical poems and treatises, as well as a number of works that reflect his subsidiary interests: mathematics and magic, the art of memory, and the so-called Lullian art.

The art of memory, which grew out of a part of ancient rhetoric, was a subject much cultivated in the Middle Ages and the Renaissance, and there are many treatises dealing with this subject, which scholars have just recently begun to study, and which probably deserve much further exploration. These efforts to devise systems for strengthening a person's memory had a very great practical importance in a period when scholars and men of affairs could not rely as heavily as nowadays on the help of indexes and reference works, and when the ready mastery of knowledge and information was considered a necessary criterion of competence, not only in speeches and disputations but also in many professional activities.

The Lullian art, named after its inventor, the fourteenth-century Catalan philosopher Ramon Lull, was a general scheme of knowledge based on a number of simple terms and propositions, and it was Lull's claim that through appropriate methods of combination this art would lead to the discovery and demonstration of all other knowledge. The method was illustrated by the use of letters, figures, and other symbols, which represented the basic concepts and their combinations. The Lullian art attracted the interest of many thinkers and scholars down to Leibniz, and it is obviously, at least in its claims if not in its achievements, a forerunner of modern symbolic logic. For Bruno, the art of memory and the Lullian art were not merely the subjects of his intellectual curiosity, but also a means of livelihood, for he seems to have instructed his private pupils mainly in these two arts. This side of Bruno's work is less well known, and a detailed study of it has been attempted only in recent years.

Bruno's thought shows many traits of genuine originality, yet at the same time he is indebted to a variety of sources. In spite of his double polemic against the grammarians and the scholastics, he owed much to his humanist education as well as to his Aristotelian and scholastic training. His doctrine of heroic love, which forms the center of his famous Eroici furori, is heavily indebted to Ficino, and it has been recently shown that this work belongs to the literary and intellectual tradition of Platonist love treatises, which occupied a rather large place in sixteenth-century thought and literature [John C. Nelson, Renaissance Theory of Love, 1958]. In his metaphysics, Bruno was strongly influenced by Plotinus and Cusanus, whereas his cosmology is based on Lucretius and Copernicus.

Many historians have discovered serious inconsistencies in Bruno's thought, and some scholars have tried to account for them on chronological grounds, assuming that his philosophical thought underwent a certain development. Without excluding such a development, I am inclined to think that from the time of his Italian dialogues his basic position remained unchanged, and that a few ambiguities, oscillations, and logical difficulties are inherent in this very position. At least on one important point that is unclear in Bruno's published writings, a recently discovered document from his last years throws a good deal of light.

Some of Bruno's chief ethical doctrines are contained in his famous Eroici furori, a group of dialogues in which the recital and interpretation of a series of poems by Bruno and others, and the explanation of a number of symbolic mottos and devices, occupy a large place, interrupting as well as enlivening the presentation of the chief philosophical ideas. In a free variation upon the common theme of Platonizing love treatises, Bruno opposes heroic love and frenzy to vulgar love. Heroic love has a divine object, and leads the soul in a gradual ascent from the sense world through intelligible objects toward God. The union with God, which is the ultimate and infinite goal of our will and intellect, cannot be attained during the present life. Hence heroic love is for the philosopher a continuous torment. But it derives an inherent nobility and dignity from its ultimate goal, which will be reached after death. It is this emphasis on the suffering which accompanies the unfulfilled heroic love during the present life that distinguishes Bruno's theory from that of most previous writers on the subject, and this may also explain why he chose to call the higher love heroic rather than divine.

A more central aspect of Bruno's thought is expressed in his dialogue De la causa, principio e uno, in which some of his basic metaphysical ideas are discussed. He starts from the fundamental notion that God must be conceived as a substance, and His effects as accidents. This is a complete reversal of the traditional Aristotelian notion of substance, according to which the term substance had always been applied to particular sense objects, whereas their permanent or passing attributes had been called accidents. For Bruno, there remains only one substance, namely God, and all particular objects, far from being substances, become accidents, that is, passing manifestations of that single substance. This notion resembles in many ways that of Spinoza, and it has often been asserted that Spinoza owed this basic conception to Bruno, although there seems to be no tangible evidence that Spinoza was familiar with Bruno's thought or writings.

In order to know God, Bruno continues, we must know His image, nature. In pursuing this task, Bruno proceeds to apply to the universe the four causes that in Aristotle and his school had merely served as contributing factors in the attempt to understand particular objects or phenomena. Developing some occasional remarks in Aristotle, Bruno divides the four causes into two groups, one of which he calls causes in the stricter sense of the word, and the other, principles. Form and matter are principles because they are intrinsic to their effect, whereas efficient and final cause are external to their effect. He then identifies the efficient cause of the world with the universal intellect, which is the highest faculty of the world soul. He is drawing here on Plotinian notions, and there is no evidence that he is identifying the world soul or its intellect with God. On the contrary, he explicitly distinguishes this world intellect from the divine intellect, and states that it contains in itself all forms and species of nature, just as our intellect contains in itself all its concepts. Working as an internal artist, this world intellect produces out of matter all material forms, which are images derived from its own internal species. The final cause of the world, on the other hand, is nothing but its own perfection.

The principles, that is, internal constituents, of nature are form and matter. They correspond in name to Aristotle's formal and material cause, but are in fact conceived along Plotinian lines. Bruno asserts that the form coincides to a certain extent with the soul, insofar as every form is produced by a soul. For all things are animated by the world soul, and all matter is everywhere permeated by soul and spirit. Thus it may be said that the world soul is the constituent formal principle of the world, just as matter is its constituent material principle. The world is thus a perpetual spiritual substance that merely appears in different forms.

In this way, form and matter are both perpetual substances and principles, and mutually determine each other, whereas the bodies composed of form and matter are perishable, and must be regarded not as substances but as accidents. Bruno thus seems to conceive of particular things as resulting from a changing interpenetration of two universal principles, and in this suggestive and original view also lies the basic difficulty of his philosophy.

In God, Bruno goes on to say, form and matter, actuality and potentiality, coincide. In what appears to be an important modification of his previous statements, he says that also in the universe there is only one principle, which is both formal and material, and thus the universe, considered in its substance, is only one. This one principle, taken with its two aspects, is said to constitute both all corporeal and all incorporeal beings. Bruno here seems to follow the so-called universal hylemorphism of Avicebron, who, too, composes all incorporeal beings of form and matter. This statement reveals still another basic ambiguity, which Bruno had inherited from Cusanus and other earlier philosophers, and which he never completely overcomes, at least in this work. That is, in speaking about nature and the universe, Bruno seems to think primarily in terms of the physical universe, but at the same time he includes in the universe all incorporeal beings except God. Speaking of matter, he insists that it is not merely negative, but contains in itself all forms, thus taking up a theory of Averroes, and departing from both Aristotle and Plotinus, who had thought of matter as pure potentiality.

Identifying the universe with the substance that comprises both form and matter, Bruno states that the universe is one and infinite, that it is being, true and one, whereas all particular things are mere accidents and subject to destruction. There is no plurality of substances in the world, but merely a plurality of manifestations of a single substance. The plurality of things is only apparent and belongs to the surface grasped by our senses, whereas our mind grasps, beyond this surface, the one substance in which all apparent contrasts coincide. This substance is true and good, it is both matter and form, and in it actuality and potentiality are no longer different from each other. In such formulas the distinction between the universe and God seems to disappear, but in one important passage Bruno differentiates between the physical universe known by the philosophers and the archetypal universe believed in by the theologians.

He thus presents us with an impressive and original vision of reality, but if we compare the various statements contained in the dialogue, a few basic ambiguities remain. Form and matter are clearly universal principles for Bruno, but he treats them sometimes as distinct and sometimes as identical, or rather as two aspects of the same principle. The physical and the metaphysical universe are sometimes identified, and sometimes quite clearly distinguished. Finally, the universe is sometimes treated as an image of God, and as distinct from Him, whereas at times this distinction tends to disappear.

Students of Bruno have tried to cope with these difficulties in a variety of ways. Some have emphasized one set of statements over the other, thus making of Bruno either a Platonist metaphysician or an outright pantheist. Those who have been willing to admit the ambiguities present in his work have often considered the extreme pantheist position to be his true position, and the dualist statements to be concessions made to popular opinion or potential censors or critics. Others have regarded pantheism as the logical consequence of his position, which he came to adopt gradually, the dualist statements representing a mere residual of his earlier views. This last opinion seems to be the soundest of the ones we have cited. However, I am more inclined to think that Bruno had a vision that was not completely expressible in terms of these antitheses, and that he was quite willing to accept the dilemma, that is, both horns of it, as a paradox and an approximation, without wishing to be pushed into a more extreme position. It is no doubt true that in comparison with his favourite sources, Plotinus and Cusanus, Bruno goes much further in the direction of a pantheistic or immanentistic conception. Yet I doubt very much that he wanted to be an extreme pantheist or naturalist. In one of his latest statements, he tries to show that individual minds are particular manifestations of the universal mind, just as particular bodies are manifestations of universal matter. This statement is a welcome addition to his other writings, in which this particular doctrine is not so clearly stated. It also shows that his position was closer to Cusanus and to the dualistic passages in his dialogues than many interpreters have been willing to admit.

No less interesting and historically significant than Bruno's metaphysics is his conception of the physical universe as we find it developed in his dialogue De l'infinito, unirerso e mondi. In this work, Bruno restates the Copernican system of the universe, and gives it for the first time a philosophical meaning. His chief emphasis is on the infinity of the universe as a whole, as against the innumerable finite worlds that are contained in it. This distinction between the universe and the worlds is borrowed from Lucretius, as is the notion of the infinity of the universe, which is not found in Copernicus at all. We now know that in the sixteenth century the infinity of the physical universe was asserted by Thomas Digges, prior to Bruno, but it is not certain that Bruno was familiar with the writings of this predecessor. We might also compare the view of Patrizi, who assumed an infinite external void surrounding our finite world. For Bruno, there are many such worlds as ours, and the universe outside our world is not a void. Moreover, unlike Patrizi, he conceives our world or solar system according to the system of Copernicus. He further insists that this infinity of the universe cannot be perceived by the senses, but is disclosed by the judgment of reason, thus reverting to Democritus from the sensationalism of the Epicureans and Telesio.

The infinite universe is for Bruno the image of an infinite God. In this context, at least, he clearly distinguishes between God and the universe, and his position may be compared with that of Cusanus. Yet whereas Cusanus reserves true infinity for God alone, Bruno uses the relation between the universe and God as an argument for the infinity of the former. Since God is infinite, also the universe must be infinite, although in a different sense.

As for Patrizi and others, the stars are no longer attached to rigid spheres, but move freely in the infinite space. Yet in accordance with the Neoplatonic tradition, and with a view adopted by most medieval Aristotelians, Bruno assigns the cause for the motion of the stars to their internal principles or souls. The earth is also in motion, and may hence be considered as one of the stars. Only the universe as a whole is at rest, whereas all particular worlds contained in it are in motion. The universe as a whole has no absolute center and no absolute direction; that is, we cannot talk of an upward or a downward direction in an absolute sense. Gravity and lightness have merely a relative meaning with reference to the parts of the universe toward which a given body is moving. This view of Bruno's may be characterized as half-Aristotelian. That is, in his denial of an absolute center, Bruno repeats a formula of Cusanus, interpreting it in a Lucretian sense. In his denial of an absolute direction, he follows the atomists against Aristotle; but in retaining a relative direction, and, above all, in retaining the distinction between gravity and lightness, he is still under the spell of Aristotelian physics.

The individual stars, Bruno argues, are subject to continual change through the influx and efflux of atoms, but persist through some internal or external force. The notion of influx and efflux is again based on atomism, and the notion that the stars are subject to change is another important departure from Aristotelian cosmology, in which the celestial objects, as distinct from the sublunar ones, are considered unchangeable and incorruptible. Yet the internal force seems to be a Neoplatonic rather than an atomistic conception. Bruno knows that the fixed stars are at varying distances from us, and thus discards the traditional notion of a single sphere of fixed stars. He thinks that the entire universe is filled with aether even in the so-called empty spaces between the stars. All stars in the universe are divided into two basic groups, which he calls suns and earths. The prevailing element of the former is fire, of the latter, water. Our earth is like a star, and when seen from the outside, it shines like the other stars. Bruno also assumes that the various worlds outside our own are inhabited. He denies the existence of elementary spheres, thus rejecting another basic conception of traditional Aristotelian cosmology, and calls the notion of a hierarchy of nature a mere product of the imagination.

Bruno's cosmology is quite suggestive, and it anticipates in a number of ways the conception of the universe as it was to be developed by modern physics and astronomy. He is not only the first major philosopher who adopted the Copernican system, but also one of the first thinkers who boldly discarded such time-honored notions as the radical distinction between things celestial and earthly, and the hierarchical view of nature. Being aware of the novelty of his view, he does not spare Aristotle or his followers, whom he pursues with a series of polemical attacks. The fact that Bruno still retains some residuals of Aristotelian physics should not be exaggerated, and it should have been expected in any case. On the other hand, it has been rightly stressed that he was a forerunner, but not a founder, of modern science and philosophy. He was unaware of the role that mathematics and experimental observation were to play in modern science, and did not develop a precise method by which his assertions might have been tested or demonstrated. His merit and his limitation lie in the fact that, through his intuition and vision, he anticipated a number of ideas that resemble those which later centuries were to adopt and to develop on the basis of much more solid evidence. Yet the more we are inclined to extol the role of imagination in the sciences, alongside that of empirical observation and logical deduction, the more we should appreciate the contribution made by such thinkers as Bruno.

The extent of Bruno's influence during the following centuries is hard to estimate. His condemnation and terrible end made it impossible for any Catholic scholar to read or cite him overtly, and even in Protestant countries his works seem to have had a rather limited circulation for a long time. Yet Galileo could have read Bruno long before the latter was condemned, and the resemblance between certain passages in Galileo and Bruno that deal with the place of the earth in the universe is so great that it may not be incidental after all. I am also inclined to see a connection between Bruno and Spinoza, for the conception of the relation between God and particular things as substance and accidents is too similar and too unusual to be a mere coincidence. Aside from many other differences, it was quite natural for Spinoza to replace Bruno's two basic principles, form (or soul) and matter, which have a Neoplatonic, and if you wish an Aristotelian, origin, with the attributes of thought and extension, which are derived from the system of Descartes. I cannot discuss the question whether the theory of monads, as developed in some of Bruno's Latin writings, may have had an influence on Leibniz.