PLANETS, STARS, AND ORBS

PLANETS, STARS, AND ORBS The Medieval Cosmos, 1200 1687 EDWARD GRANT Indiana University v CAMBRIDGE UNIVERSITY PRESS

Contents Illustrations Preface Acknowledgments Abbreviations INTRODUCTION: SCOPE, SOURCES, AND page xv xvii xx xxii SOCIAL CONTEXT I. Pierre Duhem, medieval cosmology and the scope of the present study 3 I. Duhem and Le Systeme du monde 3 II. The scope of the present study 5 i. The three parts 5 2. Terminology 7 III. Temporal limits 9 2. The sources of cosmology in the late Middle Ages 11 I. The twofold significance of the term "sources" 11 II. The cosmological inheritance 11 i. Latin cosmological literature from the early Middle Ages 11 2. Greco-Arabic sources translated in the twelfth and thirteenth centuries 12 3. The advent of printing and Greco-Latin additions to the medieval heritage in the fifteenth and sixteenth centuries 17 III. The medieval Latin literature of scholastic cosmology, 1200-1687 19 1. The medieval university, Aristotle, and the use of the terms "natural philosophy," "scholastic," and "Aristotelian" 19 2. The basic form of cosmological literature: the questiones 23 3. Questions and commentaries on Aristotle's De caelo (On the Heavens) 27 4. Questions and commentaries on cosmological themes in Aristotle's other physical treatises 31 5. Questions on the Sentences of Peter Lombard 31 vu

Vlll CONTENTS 6. Other relevant literature 33 7. Technical astronomical literature as a source for scholastic cosmology 36 IV. Idiosyncratic cosmologies 39 3. The social and institutional matrix of scholastic cosmology 46 I. Social factors 46 II. General societal influences 47 III. The influence of university and church 50 1. The 1260s and 1270s prior to the Condemnation of 1277 50 2. The Condemnation of 1277 53 IV. The intellectual tradition as social context 56 V. The impact of medieval cosmology on society 59 PART I THE COSMOS AS A WHOLE AND WHAT, IF ANYTHING, LIES BEYOND 4. Is the world eternal, without beginning or end? 63 I. Did the world begin by creation, or has it existed without a beginning through an eternal past? 63 II. Bonaventure's defense of temporal creation and rejection of creation from eternity 67 III. On the philosophical and theological reconciliation of creation and eternity 70 IV. Is the world incorruptible, or will it cease to be? 77 V. Medieval ambivalence 82 5. The creation of the world ' 83 I. Was creation simultaneous, in six days, or both? 83 II. Was creation from nothing? 89 III. Scriptural exegesis: Augustine and Thomas Aquinas 90 IV. On the first four days of creation 91 V. What is the heaven created on the first day? 94 VI. On the firmament of the second day 95 1. The firmament as air 96 2. The firmament as a single heaven embracing all the planets and the fixed stars 97 3. The firmament as the sphere of the fixed stars 100 VII. On the waters above the firmament: the crystalline heaven 103 VIII. The celestial luminaries created in the firmament on the fourth day 104 6. The finitude, shape, and place of the world 106 I. On the finitude of the world 106 II. On the shape of the world 113 III. Are the outermost sphere, and the world itself, in a place? 122

CONTENTS i. Aristotle on the place of a body 122 2. Responses to the problem 124 7. The perfection of the world 136 I. Is the world perfect? 136 II. Could God make our world more perfect? 140 1. Increasing the perfection of the world through its parts 141 2. Increasing the perfection of the world through the order of its parts 146 3. Increasing the perfection of the world by the improvement of its goal or purpose 146 4. Does the world's perfection reside in its diversity or uniformity? 148 8. The possibility of other worlds 150 I. Plurality of worlds before 1277 150 II. Plurality of worlds after 1277 155 1. A plurality of simultaneous concentric and eccentric worlds 156 2. A plurality of simultaneous worlds, each separate and distinct from the others 157 9. Extracosmic void Space 169 I. Independent extracosmic void space 170 II. God-filled extracosmic void Space 173 III. The meaning of "imaginary" in the expression "imaginary infinite space" 177 PART II THE CELESTIAL REGION 10. The incorruptibility of the celestial region 189 I. Aristotle on celestial incorruptibility 191 II. The medifeval defense of celestial incorruptibility 193 1. Theory 193 2. Experience 203 III. Scholastic interpretations of celestial incorruptibility in the sixteenth and seventeenth centuries 205 1. The traditional scholastic defense of celestial incorruptibility 206 2. Celestial incorruptibility and the discoveries of Tycho and Galileo 210 3. The scholastic reaction to the discoveries of Tycho and Galileo 211 11. Celestial perfection 220 I. Intracelestial perfection 220 1. Are all celestial bodies in the same irreducible species? 220 2. Aristotle on intracelestial degrees of perfection 223 ix

X CONTENTS 3. Medieval interpretations: Aquinas, Buridan, and Oresme 225 4. Continuation and extension of medieval interpretations in the sixteenth and seventeenth centuries 231 5. Challenge to the idea of intracelestial, hierarchical perfection 234 II. Celestial bodies compared to animate and inanimate sublunar bodies 235 1. Two major opinions comparing the celestial region to living things 236 2. A big departure: The earth, with the life on it, is more perfect than the Sun 239 12. On celestial matter: Can it exist in a changeless State? 244 I. That matter does not exist in the heavens 245 II. Two rival theories in support of the existence of celestial matter 250 1. Aquinas and Galileo: Celestial and terrestrial matter differ 250 2. Aegidius and Ockham: Celestial and terrestrial matter are identical 254 III. Celestial matter in the late sixteenth and the seventeenth Century 259 1. The focus of the debate: Thomas or Aegidius? 259 2. Scholastic repudiation of incorruptibility: the corruptibility of celestial matter 262 IV. Some concluding observations about celestial matter and incorruptibility 268 13. The mobile celestial orbs: concentrics, eccentrics, and epicycles 271 I. One heaven (or sphere) or many? 271 II. Concentric versus eccentric orbs 275 1. Aristotle's System of concentric spheres 275 2. Ptolemy's System of eccentric spheres 277 3. The System of eccentrics: Roger Bacon 279 4. The System of eccentrics: Pierre d'ailly 281 5. Epicycles 283 6. The great compromise: the three-orb System 284 III. Cosmological problems with eccentrics and epicycles 286 1. Vacua and condensation and rarefaction in the heavens 288 2. Are the celestial spheres continuous or contiguous? 289 3. The rejection of continuity and contiguity: the assumption of matter between two orbs 293

CONTENTS 4. If eccentrics exist, can the earth lie at the center of the world? 296 5. Eccentrics and the problem of a plurality of centers 297 6. Would planets move with rectilinear motion if eccentrics and epicycles existed? 298 7. The problem with epicycles 299 8. Summary of differences with Aristotle 302 9. On the physical nature of eccentrics 303 10. On the assumed physical reality of eccentrics and epicycles 307 IV. On the number and order of the mobile heavenly orbs 308 1. On the order of the heavens 308 2. The number of orbs 315 14. Are the heavens composed of hard orbs or a fluid substance?, 324 I. Modern interpretations of medieval orbs 324 II. The meaning of the term solidum in the Middle Ages 328 III. The three major positions 331 IV. The crystalline orb 332 V. The firmament and the planetary orbs 334 VI. On the difficulties of determining whether natural philosophers assumed hard or fluid orbs in the late Middle Ages 342 VII. When did "solid orb" become synonymous with "hard orb"? 345 VIII. The scholastic reaction to Tycho Brahe: hard orbs or fluid heavens, or both, in the late sixteenth and the seventeenth Century? 348 1. Scholastic arguments for fluid heavens 351 2. Scholastic arguments for hard spheres 361 IX. The diversity of opinion 368 15. The immobile orb of the cosmos: the empyrean heaven 371 I. Features and properties of the empyrean heaven 371 II. Arguments for and against an immobile sphere 374 1. The arguments against 374 2. In defense of an empyrean sphere 376 III. Can the empyrean heaven influence the terrestrial region? 378 IV. Concepts of the empyrean orb in the late sixteenth and the seventeenth Century 382 1. Does the empyrean heaven cause terrestrial effects? 384 2. The Status of the empyrean heaven 387 XI

XU CONTENTS 16. Celestial light 390 I. The sources 390 II. Lux and lumett 392 III. Are the stars and planets self-luminous, or do they receive their light from the Sun? 393 1. The Sun as sole source of celestial light 395 2. That the celestial bodies have some or all of their light from themselves 400 3. Seventeenth-century scholastic interpretations and the new discoveries 402 IV. Is the light of the stars and planets of the same species? 419 V. Celestial light as a mix of old and new 420 17. The properties and qualities of celestial bodies, and the dimensions of the world 422 I. The celestial ether 422 II. Whether all celestial orbs and bodies belong to the same species 428 III. The dimensions of the world and its celestial bodies 433 IV. The properties and qualities of the stars and planets 443 1. The fixed stars 443 2. The Sun 451 3. The Moon 459 4. The other planets 466 V. Are the heavens alive? 469 1. Two senses of life 471 2. The theological reaction to the idea of living celestial bodies: the Condemnation of 1277 472 3. The intellective, or rational, soul 474 4. Heavens not really animated 486 18. On celestial motions and their causes 488 I. The kinematics of celestial motion 488 1. Uniformity and regularity 488 2. Contrary motions 497 3. On the commensurability or incommensurability of the celestial motions and the Great Year 498 II. The dynamics of celestial motion 514 1. Aristotle on internal and external celestial movers 514 2. Medieval concepts of the prime mover 517 3. Medieval concepts of the other celestial movers 523 4. External movers: intelligences (or angels) 526

CONTENTS 5. Internal movers 545 6. External and internal motive forces that act simultaneously 553 7. Al-Bitrüji and the desire to avoid contrary motions 563 8. Did angels and intelligences function as mechanical forces? 567 19. The influence of the celestial region on the terrestrial 569 I. Celestial actions and human free will 569 II. The general claim for celestial influence 570 III. The basis of belief in celestial causes of terrestrial change 571 1. The theory of celestial causation 571 2. The empirical basis for celestial causation 575 IV. Can celestial bodies generate living things? 579 V. The instrumentalities of celestial action 586 1. Motion 588 2. Light 603 3. Influence 611 VI. Universal nature and the preservation of the world 615 20. The earth and its cosmic relations: size, centrality, shape, and immobility 618 I. The size of the earth 620 II. The earth's centrality 622 1. The three centers 622 2. Does the earth move with small rectilinear motions? 624 III. The shape of the earth 626 IV. The terraqueous globe 630 1. The curious and minimal role of water in the determination of the earth's center of gravity 630 2. One center of gravity for the two separate spheres of water and earth 634 3. The terraqueous globe: Earth and water form one sphere, with one center of gravity 635 V. The earth's immobility: rejection of a daily axial rotation 637 1. The medieval scholastic case for and against the earth's axial rotation 639 2. The debate over the earth's immobility after Copernicus 647 3. Scholastic attitudes toward the heliocentric system 672 xm

XIV CONTENTS Conclusion: Five centuries of scholastic cosmology 675 I. Tradition 675 II. Innovation 676 Appendix I: Catalog of Questions on Medieval Cosmology, 1200-1687 681 Part I. The world as a whole 682 Part II. The celestial region 694 Part III. Questions relevant to the celestial and terrestrial regions 719 Part IV. The terrestrial [or sublunar] region 731 Appendix II: The anatomy of medieval cosmology the significance of the "Catalog of Questions" in Appendix I 742 I. Chronological list of authors and works on which the "Catalog of Questions" is based 742 II. Authors 747 III. Works 751 IV. The questions 754 1. Organization of questions 755 2. On similarities and differences among questions 756 3. Criteria for inclusion and exclusion of questions 757 4. On the adequacy of the sample of authors, works, and questions 761 5. What the "Catalog of Questions" reveals 762 6. Within the compass of a single treatise, were some questions judged more important than others? 766 Bibliography 776 Index 798