part or inadequately.
Note.--Here, I doubt not, readers will come to a stand, and
will call to mind many things which will cause them to hesitate;
I therefore beg them to accompany me slowly, step by step, and
not to pronounce on my statements, till they have read to the
end.
PROP. XII. Whatsoever comes to pass in the object of the idea,
which constitutes the human mind, must be perceived by the human
mind, or there will necessarily be an idea in the human mind of
the said occurrence. That is, if the object of the idea
constituting the human mind be a body, nothing can take place in
that body without being perceived by the mind.
Proof.--Whatsoever comes to pass in the object of any idea,
the knowledge thereof is necessarily in God (II. ix. Coroll.), in
so far as he is considered as affected by the idea of the said
object, that is (II. xi.), in so far as he constitutes the mind
of anything. Therefore, whatsoever takes place in the object
constituting the idea of the human mind, the knowledge thereof is
necessarily in God, in so far as he constitutes the essence of
the human mind; that is (by II. xi. Coroll.) the knowledge of
the said thing will necessarily be in the mind, in other words
the mind perceives it.
Note.--This proposition is also evident, and is more clearly
to be understood from II. vii., which see.
PROP. XIII. The object of the idea constituting the human mind
is the body, in other words a certain mode of extension which
actually exists, and nothing else.
Proof.--If indeed the body were not the object of the human
mind, the ideas of the modifications of the body would not be in
God (II. ix. Coroll.) in virtue of his constituting our mind, but
in virtue of his constituting the mind of something else; that
is (II. xi. Coroll.) the ideas of the modifications of the body
would not be in our mind: now (by II. Ax. iv.) we do possess the
idea of the modifications of the body. Therefore the object of
the idea constituting the human mind is the body, and the body as
it actually exists (II. xi.). Further, if there were any other
object of the idea constituting the mind besides body, then, as
nothing can exist from which some effect does not follow (I.
xxxvi.) there would necessarily have to be in our mind an idea,
which would be the effect of that other object (II. xi.); but
(I. Ax. v.) there is no such idea. Wherefore the object of our
mind is the body as it exists, and nothing else. Q.E.D.
Note.--We thus comprehend, not only that the human mind is
united to the body, but also the nature of the union between mind
and body. However, no one will be able to grasp this adequately
or distinctly, unless he first has adequate knowledge of the
nature of our body. The propositions we have advanced hitherto
have been entirely general, applying not more to men than to
other individual things, all of which, though in different
degrees, are animated.[3] For of everything there is necessarily
an idea in God, of which God is the cause, in the same way as
there is an idea of the human body; thus whatever we have
asserted of the idea of the human body must necessarily also be
asserted of the idea of everything else. Still, on the other
hand, we cannot deny that ideas, like objects, differ one from
the other, one being more excellent than another and containing
more reality, just as the object of one idea is more excellent
than the object of another idea, and contains more reality.
[3] "Animata"
Wherefore, in order to determine, wherein the human mind
differs from other things, and wherein it surpasses them, it is
necessary for us to know the nature of its object, that is, of
the human body. What this nature is, I am not able here to
explain, nor is it necessary for the proof of what I advance,
that I should do so. I will only say generally, that in
proportion as any given body is more fitted than others for doing
many actions or receiving many impressions at once, so also is
the mind, of which it is the object, more fitted than others for
forming many simultaneous perceptions; and the more the actions
of the body depend on itself alone, and the fewer other bodies
concur with it in action, the more fitted is the mind of which it
is the object for distinct comprehension. We may thus recognize
the superiority of one mind over others, and may further see the
cause, why we have only a very confused knowledge of our body,
and also many kindred questions, which I will, in the following
propositions, deduce from what has been advanced. Wherefore I
have thought it worth while to explain and prove more strictly my
present statements. In order to do so, I must premise a few
propositions concerning the nature of bodies.
AXIOM I. All bodies are either in motion or at rest.
AXIOM II. Every body is moved sometimes more slowly,
sometimes more quickly.
LEMMA I. Bodies are distinguished from one another in
respect of motion and rest, quickness and slowness, and not in
respect of substance.
Proof.--The first part of this proposition is, I take it,
self--evident. That bodies are not distinguished in respect of
substance, is plain both from I. v. and I. viii. It is brought
out still more clearly from I. xv, note.
LEMMA II. All bodies agree in certain respects.
Proof.--All bodies agree in the fact, that they involve the
conception of one and the same attribute (II., Def. i.).
Further, in the fact that they may be moved less or more quickly,
and may be absolutely in motion or at rest.
LEMMA III. A body in motion or at rest must be determined to
motion or rest by another body, which other body has been
determined to motion or rest by a third body, and that third
again by a fourth, and so on to infinity.
Proof.--Bodies are individual things (II., Def. i.), which
(Lemma I.) are distinguished one from the other in respect to
motion and rest; thus (I. xxviii.) each must necessarily be
determined to motion or rest by another individual thing, namely
(II. vi.), by another body, which other body is also (Ax. i.) in
motion or at rest. And this body again can only have been set in
motion or caused to rest by being determined by a third body to
motion or rest. This third body again by a fourth, and so on to
infinity. Q.E.D.
Corollary.--Hence it follows, that a body in motion keeps in
motion, until it is determined to a state of rest by some other
body; and a body at rest remains so, until it is determined to a
state of motion by some other body. This is indeed self--evident.
For when I suppose, for instance, that a given body, A, is at
rest, and do not take into consideration other bodies in motion,
I cannot affirm anything concerning the body A, except that it is
at rest. If it afterwards comes to pass that A is in motion,
this cannot have resulted from its having been at rest, for no
other consequence could have been involved than its remaining at
rest. If, on the other hand, A be given in motion, we shall, so
long as we only consider A, be unable to affirm anything
concerning it, except that it is in motion. If A is
subsequently found to be at rest, this rest cannot be the result
of A's previous motion, for such motion can only have led to
continued motion; the state of rest therefore must have resulted
from something, which was not in A, namely, from an external
cause determining A to a state of rest.
Axiom I.--All modes, wherein one body is affected by another
body, follow simultaneously from the nature of the body affected
and the body affecting; so that one and the same body may be
moved in different modes, according to the difference in the
nature of the bodies moving it; on the other hand, different
bodies may be moved in different modes by one and the same body.
Axiom II.--When a body in motion impinges on another body at
rest, which it is unable to move, it recoils, in order to
continue its motion, and the angle made by the line of motion in
the recoil and the plane of the body at rest, whereon the moving
body has impinged, will be equal to the angle formed by the line
of motion of incidence and the same plane.
So far we have been speaking only of the most simple bodies,
which are only distinguished one from the other by motion and
rest, quickness and slowness. We now pass on to compound bodies.
Definition.--When any given bodies of the same or different
magnitude are compelled by other bodies to remain in contact, or
if they be moved at the same or different rates of speed, so that
their mutual movements should preserve among themselves a certain
fixed relation, we say that such bodies are in union, and that
together they compose one body or individual, which is
distinguished from other bodies by the fact of this union.
Axiom III.--In proportion as the parts of an individual, or a
compound body, are in contact over a greater or less superficies,
they will with greater or less difficulty admit of being moved
from their position; consequently the individual will, with
greater or less difficulty, be brought to assume another form.
Those bodies, whose parts are in contact over large superficies,
are called hard; those, whose parts are in contact over small
superficies, are called soft; those, whose parts are in motion
among one another, are called fluid.
LEMMA IV. If from a body or individual, compounded of
several bodies, certain bodies be separated, and if, at the same
time, an equal number of other bodies of the same nature take
their place, the individual will preserve its nature as before,
without any change in its actuality (forma).
Proof.--Bodies (Lemma i.) are not distinguished in respect of
substance: that which constitutes the actuality (formam) of an
individual consists (by the last Def.) in a union of bodies; but
this union, although there is a continual change of bodies, will
(by our hypothesis) be maintained; the individual, therefore,
will retain its nature as before, both in respect of substance
and in respect of mode. Q.E.D.
LEMMA V. If the parts composing an individual become greater
or less, but in such proportion, that they all preserve the same
mutual relations of motion and rest, the individual will still
preserve its original nature, and its actuality will not be
changed.
Proof.--The same as for the last Lemma.
LEMMA VI. If certain bodies composing an individual be
compelled to change the motion, which they have in one direction,
for motion in another direction, but in such a manner, that they
be able to continue their motions and their mutual communication
in the same relations as before, the individual will retain its
own nature without any change of its actuality.
Proof.--This proposition is self--evident, for the individual
is supposed to retain all that, which, in its definition, we
spoke of as its actual being.
LEMMA VII. Furthermore, the individual thus composed
preserves its nature, whether it be, as a whole, in motion or at
rest, whether it be moved in this or that direction; so long as
each part retains its motion, and preserves its communication
with other parts as before.
Proof.--This proposition is evident from the definition of an
individual prefixed to Lemma iv.
Note.--We thus see, how a composite individual may be affected
in many different ways, and preserve its nature notwithstanding.
Thus far we have conceived an individual as composed of bodies
only distinguished one from the other in respect of motion and
rest, speed and slowness; that is, of bodies of the most simple
character. If, however, we now conceive another individual
composed of several individuals of diverse natures, we shall find
that the number of ways in which it can be affected, without
losing its nature, will be greatly multiplied. Each of its parts
would consist of several bodies, and therefore (by Lemma vi.)
each part would admit, without change to its nature, of quicker
or slower motion, and would consequently be able to transmit its
motions more quickly or more slowly to the remaining parts. If
we further conceive a third kind of individuals composed of
individuals of this second kind, we shall find that they may be
affected in a still greater number of ways without changing their
actuality. We may easily proceed thus to infinity, and conceive
the whole of nature as one individual, whose parts, that is, all
bodies, vary in infinite ways, without any change in the
individual as a whole. I should feel bound to explain and
demonstrate this point at more length, if I were writing a
special treatise on body. But I have already said that such is
not my object; I have only touched on the question, because it
enables me to prove easily that which I have in view.
POSTULATES
I. The human body is composed of a number of individual
parts, of diverse nature, each one of which is in itself
extremely complex.
II. Of the individual parts composing the human body some
are fluid, some soft, some hard.
III. The individual parts composing the human body, and
consequently the human body itself, are affected in a variety of
ways by external bodies.
IV. The human body stands in need for its preservation of a
number of other bodies, by which it is continually, so to speak,
regenerated.
V. When the fluid part of the human body is determined by an
external body to impinge often on another soft part, it changes
the surface of the latter, and, as it were, leaves the impression
thereupon of the external body which impels it.
VI. The human body can move external bodies, and arrange
them in a variety of ways.
PROP. XIV. The human mind is capable of perceiving a great
number of things, and is so in proportion as its body is capable
of receiving a great number of impressions.
Proof.--The human body (by Post. iii. and vi.) is affected in
very many ways by external bodies, and is capable in very many
ways of affecting external bodies. But (II. xii.) the human
mind must perceive all that takes place in the human body; the
human mind is, therefore, capable of perceiving a great number of
things, and is so in proportion, &c. Q.E.D.
PROP. XV. The idea, which constitutes the actual being of the
human mind, is not simple, but compounded of a great number of
ideas.
Proof.--The idea constituting the actual being of the human
mind is the idea of the body (II. xiii.), which (Post. i.) is
composed of a great number of complex individual parts. But
there is necessarily in God the idea of each individual part
whereof the body is composed (II. viii. Coroll.); therefore
(II. vii.), the idea of the human body is composed of these
numerous ideas of its component parts. Q.E.D.
PROP. XVI. The idea of every mode, in which the human body is
affected by external bodies, must involve the nature of the human
body, and also the nature of the external body.
Proof.--All the modes, in which any given body is affected,
follow from the nature of the body affected, and also from the
nature of the affecting body (by Ax. i., after the Coroll. of
Lemma iii.), wherefore their idea also necessarily (by I. Ax.
iv.) involves the nature of both bodies; therefore, the idea of
every mode, in which the human body is affected by external
bodies, involves the nature of the human body and of the external
body. Q.E.D.
Corollary I.--Hence it follows, first, that the human mind
perceives the nature of a variety of bodies, together with the
nature of its own.
Corollary II.--It follows, secondly, that the ideas, which we
have of external bodies, indicate rather the constitution of our
own body than the nature of external bodies. I have amply
illustrated this in the Appendix to Part I.
PROP. XVII. If the human body is affected in a manner which
involves the nature of any external body, the human mind will
regard the said external body as actually existing, or as present
to itself, until the human body be affected in such a way, as to
exclude the existence or the presence of the said external body.
Proof.--This proposition is self--evident, for so long as the
human body continues to be thus affected, so long will the human
mind (II. xii.) regard this modification of the body--that is (by
the last Prop.), it will have the idea of the mode as actually
existing, and this idea involves the nature of the external body.
In other words, it will have the idea which does not exclude, but
postulates the existence or presence of the nature of the
external body; therefore the mind (by II. xvi., Coroll. i.) will
regard the external body as actually existing, until it is
affected, &c. Q.E.D.
Corollary.--The mind is able to regard as present external
bodies, by which the human body has once been affected, even
though they be no longer in existence or present.
Proof.--When external bodies determine the fluid parts of the
human body, so that they often impinge on the softer parts, they
change the surface of the last named (Post. v.); hence (Ax. ii.,
after the Coroll. of Lemma iii.) they are refracted therefrom in
a different manner from that which they followed before such
change; and, further, when afterwards they impinge on the new
surfaces by their own spontaneous movement, they will be
refracted in the same manner, as though they had been impelled
towards those surfaces by external bodies; consequently, they
will, while they continue to be thus refracted, affect the human
body in the same manner, whereof the mind (II. xii.) will again
take cognizance--that is (II. xvii.), the mind will again regard
the external body as present, and will do so, as often as the
fluid parts of the human body impinge on the aforesaid surfaces
by their own spontaneous motion. Wherefore, although the
external bodies, by which the human body has once been affected,
be no longer in existence, the mind will nevertheless regard them
as present, as often as this action of the body is repeated.
Q.E.D.
Note.--We thus see how it comes about, as is often the case,
that we regard as present many things which are not. It is
possible that the same result may be brought about by other
causes; but I think it suffices for me here to have indicated
one possible explanation, just as well as if I had pointed out
the true cause. Indeed, I do not think I am very far from the
truth, for all my assumptions are based on postulates, which
rest, almost without exception, on experience, that cannot be
controverted by those who have shown, as we have, that the human
body, as we feel it, exists (Coroll. after II. xiii.).
Furthermore (II. vii. Coroll., II. xvi. Coroll. ii.), we clearly
understand what is the difference between the idea, say, of
Peter, which constitutes the essence of Peter's mind, and the
idea of the said Peter, which is in another man, say, Paul. The
former directly answers to the essence of Peter's own body, and
only implies existence so long as Peter exists; the latter
indicates rather the disposition of Paul's body than the nature
of Peter, and, therefore, while this disposition of Paul's body
lasts, Paul's mind will regard Peter as present to itself, even
though he no longer exists. Further, to retain the usual
phraseology, the modifications of the human body, of which the
ideas represent external bodies as present to us, we will call
the images of things, though they do not recall the figure of
things. When the mind regards bodies in this fashion, we say
that it imagines. I will here draw attention to the fact, in
order to indicate where error lies, that the imaginations of the
mind, looked at in themselves, do not contain error. The mind
does not err in the mere act of imagining, but only in so far as
it is regarded as being without the idea, which excludes the
existence of such things as it imagines to be present to it. If
the mind, while imagining non--existent things as present to it,
is at the same time conscious that they do not really exist, this
power of imagination must be set down to the efficacy of its
nature, and not to a fault, especially if this faculty of
imagination depend solely on its own nature--that is (I. Def.
vii.), if this faculty of imagination be free.
PROP. XVIII. If the human body has once been affected by two or
more bodies at the same time, when the mind afterwards imagines
any of them, it will straightway remember the others also.
Proof.--The mind (II. xvii. Coroll.) imagines any given body,
because the human body is affected and disposed by the
impressions from an external body, in the same manner as it is
affected when certain of its parts are acted on by the said
external body; but (by our hypothesis) the body was then so
disposed, that the mind imagined two bodies at once; therefore,
it will also in the second case imagine two bodies at once, and
the mind, when it imagines one, will straightway remember the
other. Q.E.D.
Note.--We now clearly see what Memory is. It is simply a
certain association of ideas involving the nature of things
outside the human body, which association arises in the mind
according to the order and association of the modifications
(affectiones) of the human body. I say, first, it is an
association of those ideas only, which involve the nature of
things outside the human body: not of ideas which answer to the
nature of the said things: ideas of the modifications of the
human body are, strictly speaking (II. xvi.), those which involve
the nature both of the human body and of external bodies. I say,
secondly, that this association arises according to the order and
association of the modifications of the human body, in order to
distinguish it from that association of ideas, which arises from
the order of the intellect, whereby the mind perceives things
through their primary causes, and which is in all men the same.
And hence we can further clearly understand, why the mind from
the thought of one thing, should straightway arrive at the
thought of another thing, which has no similarity with the first;
for instance, from the thought of the word pomum (an apple), a
Roman would straightway arrive at the thought of the fruit apple,
which has no similitude with the articulate sound in question,
nor anything in common with it, except that the body of the man
has often been affected by these two things; that is, that the
man has often heard the word pomum, while he was looking at the
fruit; similarly every man will go on from one thought to
another, according as his habit has ordered the images of things
in his body. For a soldier, for instance, when he sees the
tracks of a horse in sand, will at once pass from the thought of
a horse to the thought of a horseman, and thence to the thought
of war, &c.; while a countryman will proceed from the thought of
a horse to the thought of a plough, a field, &c. Thus every man
will follow this or that train of thought, according as he has
been in the habit of conjoining and associating the mental images
of things in this or that manner.
PROP. XIX. The human mind has no knowledge of the body, and does
not know it to exist, save through the ideas of the modifications
whereby the body is affected.
Proof.--The human mind is the very idea or knowledge of the
human body (II. xiii.), which (II. ix.) is in God, in so far as
he is regarded as affected by another idea of a particular thing
actually existing: or, inasmuch as (Post. iv.) the human body
stands in need of very many bodies whereby it is, as it were,
continually regenerated; and the order and connection of ideas
is the same as the order and connection of causes (II. vii.);
this idea will therefore be in God, in so far as he is regarded
as affected by the ideas of very many particular things. Thus
God has the idea of the human body, or knows the human body, in
so far as he is affected by very many other ideas, and not in so
far as he constitutes the nature of the human mind; that is (by
II. xi. Coroll.), the human mind does not know the human body.
But the ideas of the modifications of body are in God, in so far
as he constitutes the nature of the human mind, or the human
mind perceives those modifications (II. xii.), and consequently
(II. xvi.) the human body itself, and as actually existing;
therefore the mind perceives thus far only the human body.
Q.E.D.
PROP. XX. The idea or knowledge of the human mind is also in
God, following in God in the same manner, and being referred to
God in the same manner, as the idea or knowledge of the human
body.
Proof.--Thought is an attribute of God (II. i.); therefore
(II. iii.) there must necessarily be in God the idea both of
thought itself and of all its modifications, consequently also of
the human mind (II. xi.). Further, this idea or knowledge of the
mind does not follow from God, in so far as he is infinite, but
in so far as he is affected by another idea of an individual
thing (II. ix.). But (II. vii.) the order and connection of
ideas is the same as the order and connection of causes;
therefore this idea or knowledge of the mind is in God and is
referred to God, in the same manner as the idea or knowledge of
the body. Q.E.D.
PROP. XXI. This idea of the mind is united to the mind in the
same way as the mind is united to the body.
Proof.--That the mind is united to the body we have shown from
the fact, that the body is the object of the mind (II. xii. and
xiii.); and so for the same reason the idea of the mind must be
united with its object, that is, with the mind in the same manner
as the mind is united to the body. Q.E.D.
Note.--This proposition is comprehended much more clearly from
what we have said in the note to II. vii. We there showed that
the idea of body and body, that is, mind and body (II. xiii.),
are one and the same individual conceived now under the attribute
of thought, now under the attribute of extension; wherefore the
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500