Proof。-The human body is affected in very many ways by external bodies，and is capable in very many ways of affecting external bodies。But the human mind must per-ceive all that takes place in the human body。Therefore，the human Mind is capable of perceiving a great many things，and is the more capable as the human Body is more ca-pable。
PROP。15.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，which 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；there-fore，the idea of the human body is composed of these numerous ideas of its component parts。
PROP。16.The idea of every mode，in which the human body is affected by exter-nal bodies，must involve the nature of the human body，and also the nature of the exter-nal 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，wherefore their idea also necessarily 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。
Corollary 1.-Hence it follows，first，that the human mind perceives the nature of a variety of bodies，together with the nature of its own。
Corollary 2.-It follows，secondly，that the ideas，which we have of external bodies，indicate rather the condition of our own body than the nature of external bodies。I have amply illustrated this in the Appendix to Part I。
PROP。17.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 exist-ing，or as present to itself，until the human body be affected in such a way，as to ex-clude 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 regard this modification of the body-that is，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 ex-clude，but postulates the existence or presence of the nature of the external body；there-fore the mind will regard the external body as actually existing，until it is affected，＆c。
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 pres-ent。
PROP。18.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 remem-ber the others also。
Proof。-The mind 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 af-fected when certain of its parts are acted on by the said external body；but the body was then so disposed，that the mind imagined two bodies at once；therefore，it will now also imagine two bodies at once，and when the mind imagines one，it will straightway re-member the other。
PROP。19.The human mind has no knowledge of the body，and does not know it to exist，save through the ideas of the modifications by which the body is affected。
Proof。-The human mind is the very idea or knowledge of the human body，which is in God，in so far as he is regarded as affected by another idea of a particular thing ac-tually existing；or，inasmuch as the human body stands in need of very many bodies whereby，it is，as it were，continually regenerated；and the order and connection of ide-as is the same as the order and connection of causes；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 affect-ed by very many other ideas，and not in so far as he constitutes the nature of the human mind；that is，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，and consequently the human body itself，and as actually existing；therefore the mind perceives thus far only the hu-man body。
PROP。20.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；therefore there must necessarily be in God the idea both of thought itself and of all its modifications，consequently also of the hu-man mind。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。But 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。
PROP。21.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；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。
PROP。22.The human mind perceives not only the modifications of the body，but also the ideas of such modification。
Proof。-The ideas of the ideas of modifications follow in God in the same manner，and are referred to God in the same manner，as the ideas of the said modifications。This is proved in the same way as II。20.But the ideas of the modifications of the body are in the human mind，that is，in God，in so far as he constitutes the essence of the human mind；therefore the ideas of these ideas will be in God，in so far as he has the knowl-edge or idea of the human mind，that is，they will be in the human mind itself，which therefore perceives not only the modifications of the body，but also the ideas of such modifications。
PROP。23.The mind does not know itself，except in so far as it perceives the ide-as of the modifications of the body。
Proof。-The idea or knowledge of the mind follows in God in the same manner，and is referred to God in the same manner，as the idea or knowledge of the body。But since the human mind does not know the human body itself，that is，since the knowl-edge of the human body is not referred to God，in so far as he constitutes the nature of the human mind；therefore，neither is the knowledge of the mind referred to God，in so far as he constitutes the essence of the human mind；therefore，the human mind thus far has no knowledge of itself。Further the ideas of the modifications，whereby the body is affected，involve the nature of the human body itself，that is，they agree with the nature of the mind；wherefore the knowledge of these ideas necessarily involves knowledge of the mind；but the knowledge of these ideas is in the human mind itself；wherefore the human mind thus far only has knowledge of itself。
PROP。24.The human mind does not involve an adequate knowledge of the parts composing the human body。
Proof。-The parts composing the human body do not belong to the essence of that body，except in so far as they communicate their motions to one another in a certain fixed relation，not in so far as they can be regarded as individuals without relation to the human body。The parts of the human body are highly complex individuals，whose parts can be separated from the human body without in any way destroying the nature and dis-tinctive quality，of the latter，and they can communicate their motions to other bodies in another relation；therefore the idea or knowledge of each part will be in God，inasmuch as he is regarded as affected by another idea of a particular thing，which particular thing is prior in the order of nature to the aforesaid part。We may，affirm the same thing of each part of each individual composing the human body；therefore，the knowledge of each part composing the human body is in God，in so far as he is affected by very many ideas of things，and not in so far as he has the idea of the human body only，in other words，the idea which constitutes the nature of the human mind；therefore，the human mind does not involve an adequate knowledge of the human body。
PROP。25.The idea of each modification of the human body does not involve an adequate knowledge of the external body。
Proof。-We have shown that the idea of a modification of the human body，in-volves the nature of an external body，in so far as that external body conditions the hu-man body in a given manner。But，in so far as the external body is an individual，which has no reference to the human body，the knowledge or idea thereof is in God，in so far as God is regarded as affected by the idea of a further thing，which is naturally prior to the said external body。Wherefore an adequate knowledge of the external body is not in God，in so far as he has the idea of the modification of the human body；in other words，the idea of the modification of the human body，does not involve an adequate knowledge of the external body。
PROP。26.The human mind does not perceive any external body as actually exist-ing，except through the ideas of the modifications of its own body。
Proof。-If the human body is in no way affected by a given external body，then neither is the idea of the human body，in other words，the human mind，affected in any way by the idea of the existence of the said external body，nor does it any manner per-ceive its existence。But，in so far as the human body is affected in any way by a given external body，thus far the mind perceives that external body。
Corollary。-In so far as the human mind imagines an external body，it has not an adequate knowledge thereof。
Proof。-When the human mind regards external bodies through the ideas of the modifications of its own body，we say that it imagines；now the mind can only imagine external bodies as actually existing。Therefore，in so far as the mind imagines external bodies，it has not an adequate knowledge of them。
PROP。27.The idea of each modification of the human body does not involve an adequate knowledge of the human body itself。
Proof。-Every idea of a modification of the human body involves the nature of the human body，in so far as the human body is regarded as affected in a given manner。But，inasmuch as the human body is an individual which may be affected in many other ways，the idea of the said modification，＆c。
PROP。28.The idea of the modifications of the human body，in so far as they have reference only to the human mind，are not clear and distinct，but confused。
Proof。-The ideas of the modifications of the human body involve the nature of ex-ternal bodies as much as that of the human Body，and must involve the nature not only of the human body as a whole，but also of its parts；for the modifications are modes with which the parts of the human body，and consequently the whole body，are affected。But adequate knowledge of external bodies and of the parts composing the human body is in God，not insofar as he is considered to be affected with the human mind，but insofar as he is considered to be affected with other ideas。Therefore，these ideas of the modifica-tions，insofar as they are related only to the human mind，are like conclusions without premises，that is，they are confused ideas。
PROP。29.The idea of the idea of each modification of the human body does not involve an adequate knowledge of the human mind。
Proof。-The idea of a modification of the human body does not involve an adequate knowledge of the said body，in other words，does not adequately express its nature；that is it does not agree with the nature of the mind adequately；therefore the idea of this ide-a does not adequately express the nature of the human mind，or does not involve an ade-quate knowledge thereof。
Corollary。-Hence it follows that the human mind，when it perceives things after the common order of nature，has not an adequate but only a confused and fragmentary knowledge of itself，of its own body，and of external bodies。For the mind does not know itself，except in so far as it perceives the ideas of the modifications of body。It only perceives its own body through the ideas of the modifications，and only perceives external bodies through the same means；thus，in so far as it has such ideas of modifica-tion，it has not an adequate knowledge of itself，nor of its own body，nor of external bodies，but only a fragmentary and confused knowledge thereof。
PROP。30.We can only have a very inadequate knowledge of the duration of our body。
Proof。-The duration of our body does not depend on its essence，nor on the abso-lute nature of God。But it is conditioned to exist and operate by causes，which in their turn are conditioned to exist and operate in a fixed and definite relation by other causes，these last again being conditioned by others，and so on to infinity。The duration of our body therefore depends on the common order of nature，or the constitution of things。Now，however a thing may be constituted，the adequate knowledge of that thing is in God，in so far as he has the ideas of all things，and not in so far as he has the idea of the human body only。Wherefore the knowledge of the duration of our body is in God very inadequate，in so far as he is only regarded as constituting the nature of the human mind；that is，this knowledge is very inadequate in our mind。
PROP。31.We can only have a very inadequate knowledge of the duration of parti-cular things external to ourselves。
Proof。-Every particular thing，like the human body，must be conditioned by an-other particular thing to exist and operate in a fixed and definite relation；this other par-ticular thing must likewise be conditioned by a third，and so on to infinity。As we have shown in the foregoing proposition，from this common property of particular things，we have only a very inadequate knowledge of the duration of our body；we must draw a sim-ilar conclusion with regard to the duration of particular things，namely，that we can only have a very inadequate knowledge of the duration thereof。
Corollary。-Hence it follows that all particular things are contingent and corrupti-ble。For we can have no adequate idea of their duration，and this is what we must un-derst and by the contingency of things and possibility of their corruption。For，except in this sense，nothing is contingent。
PROP。32.All ideas，in so far as they are referred to God，are true。
Proof。-All ideas which are in God agree in every respect with their objects，there-fore they are all true。
PROP。33.There is nothing positive in ideas，which causes them to be called false。
Proof。-If this be denied，conceive，if possible，a positive mode of thinking which constitutes the form of error，or falsity。Such a mode of thinking cannot be in God；ex-ternal to God it cannot be or be conceived。Therefore there is nothing positive in ideas which causes them to be called false。
PROP。34.Every idea，which in us is absolute or adequate and perfect，is true。
Proof。-When we say that an idea in us is adequate and perfect，we say，in other words，that the idea is adequate and perfect in God，in so far as he constitutes the es-sence of our mind；consequently，we say，that such an idea is true。
PROP。35.Falsity consists in the privation of knowledge，which inadequate，frag-mentary，or confused ideas involve。
Proof。-There is nothing positive in ideas，which causes them to be called false；but falsity cannot consist in simple privation（for minds，not bodies，are said to err and to be mistaken），neither can it consist in absolute ignorance，for ignorance and error are not identical；wherefore it consists in the privation of knowledge，which inadequate，fragmentary，or confused ideas involve。
PROP。36.Inadequate and confused ideas follow by the same necessity，as ade-quate or clear and distinct ideas。
Proof。-All ideas are in God，and in so far as they are referred to God are true and adequate；therefore there are no ideas confused or inadequate，except in respect to a particular mind；therefore all ideas，whether adequate or inadequate，follow by the same necessity。
PROP。37.That which is common to all，and which is equally in a part and in the whole，does not constitute the essence of any particular thing。
Proof。-If this be denied，conceive，if possible，that it constitutes the essence of some particular thing；for instance，the essence of B。Then it cannot without B either exist or be conceived；but this is against our hypothesis。Therefore it does not appertain to B s essence，nor does it constitute the essence of any particular thing。
PROP。38.Those things，which are common to all，and which are equally in a part and in the whole，cannot be conceived except adequately。
Proof。-Let A be something，which is common to all bodies，and which is equally present in the part of any given body and in the whole。I say A cannot be conceived ex-cept adequately。For the idea thereof in God will necessarily be adequate，both in so far as God has the idea of the human body，and also in so far as he has the idea of the mod-ifications of the human body，which involve in part the nature of the human body and the nature of external bodies；that is，the idea in God will necessarily be adequate，both in so far as he constitutes the human mind，and in so far as he has the ideas，which are in the human mind。Therefore the mind necessarily perceives A adequately，and has this adequate perception，both in so far as it perceives itself，and in so far as it per-ceives its own or any external body，nor can A be conceived in any other manner。
Corollary。-Hence it follows that there are certain ideas or notions common to all men；for all bodies agree in certain respects，which must be adequately or clearly and distinctly perceived by all。
PROP。39.That，which is common to and a property of the human body and such other bodies as are wont to affect the human body，and which is present equally in each part of either，or in the whole，will be represented by an adequate idea in the mind。
Proof。-If A be that，which is common to and a property of the human body，and external bodies，and equally present in the human body and in the said external bodies，in each part of each external body and in the whole，there will be an adequate idea of A in God，both in so far as he has the idea of the human body，and in so far as he has the ideas of the given external bodies。Let it now be granted，that the human body is affect-ed by an external body through that，which it has in common therewith，namely，A；the idea of this modification will involve the property A，and therefore the idea of this modi-fication，in so far as it involves the Property A，will be adequate in God，in so far as God is affected by the idea of the human body；that is，in so far as he constitutes the nature of the human mind；therefore this idea is also adequate in the human mind。
Corollary。-Hence it follows that the mind is fitted to perceive adequately more things，in proportion as its body has more in common with other bodies。
PROP。40.Whatsoever ideas in the mind follow from ideas which are therein ade-quate，are also themselves adequate。
Proof。-This Proposition is self-evident。For when we say that an idea in the hu-man mind follows from ideas which are therein adequate，we say，in other words，that an idea is in the divine intellect，whereof God is the cause，not in so far as he is infi-nite，nor in so far as he is affected by the ideas of very many particular things，but only in so far as he constitutes the essence of the human mind。