analytic a priori (sense experience)

INNOCENT synthetic a posteriori ('rational' dreams that don't make sense)

"I + I = II" "In grasping reality professors generally make more sense than apes." "Apples are fine food" Many families mourning is not THAT different from 1 family mourning Blacks are fine people Women are beautiful and amazing independent animals

1 + 1 = me" (the egoism of the wishful dream Capitalism or 'Gold Fever') 2 apes have more voting power than 1 professor (the dream western democracy). "I own that apple tree, and manage the entire orchard (the wishful dream Industrialism) Thousands of dead by passivity is LESS BAD than 1 active murder (the dream power thinking) Kant: Blackness is ugliness and stupidity (the dreams apartheid and slavery) Kant: Marriage makes the wife servant of her husband (the wishful dream male superiority)

In this basic work Kant responds to Hume's skeptical suggestions in the "Enquiry," which deny both traditional "dogmatic" metaphysics (think of Descartes and Leibniz), and other abstract sciences, like physics and astronomy.
Kant nor Hume seem to realize that empiricism, rationalism and metaphysics are only corners of 1 out of endless thought systems. And Kant presumes that the absolute 'a priori' of rationalism are 'given from God'. That's mainly why his attempts to find compromise are difficult to grasp.
[The Joker: Few comments, trying to follow Kant's views. Descartes innocently released a dubious Technological spell. The frustrated Immanuel Kant longing for fame made it fit for general use. Like dressing everybody in one rigid uniform logic, disrepecting individual creativy. Changing the brilliant still harmless scientific guinea pig 'Deus ex Machina' into a snakelike 'Nightmare in Negligee. Brilliant but ignorant Kant COMPLETELY underestimated abstract thinking. Marx rationally INVENTED a border between 'poor' and 'rich' with Capitalism. Darwin like Kant saw ethics just as innocent ABSTRACT thought, by only stressing the physical Law of the Fittest. ].

Kant was primarily interested in knowing how we can know that two spirit dreams (events) are connected causally, rather than willing to find if 'spirits' are there.

The Englisman Hume though criticized the weird concept of causation and effect as being conservative fundamentalist Roman Christian humbug. Thus he denied 'spirit thinking' as a way to stay on the Roman Christian path.

Kant being an admiring  adversary of Hume accepted the challenge to give 'spirit thinking' (metaphysics) a clearer definition and stronger foundation. His project became to make 'spirits' scientific. That means making hosting a 'spirit' an a priori of a Christian Science.

Kant claims his system has caused a "Copernican revolution in philosophy." Remark: centuries later this was called a paradigm shift. Different from before Kant saw space and time not as properties of the world, but as merely rather general concepts given to the human mind..
Indeed Kant realized a near to total paradigm shift in the Western World.
Near to total, because Friedrich Nietzsche, Ludwig Wittgenstein and Thomas Kuhn slipped through
Kant added rational logic to sensory environment. Kant missed that nature already provided a 'logic', common sense. After Kant rational thought gradually replaced common sense in the Western World, and even started to infect neighbouring cultures.
When near to total paradigm shifts stick on 99%, then be sure that either the time was not yet ripe (Jesus and 'Love') or they contain VERY fishy elements (Kant and Abstract Thought). Evolution created an escape way.
The fishy thing was that human evolution wasn't yet prepared for artificil logics being used in social life. New ethics should be developed first.
See reviewed Western World History

In fact Kant made a brilliant observation: that in between paradigm shifts humans behave quite uniform. That's a remarkably clever insight. For instance from Euclides till Einstein we explained space with Euclidian geometry. And even Einstein didn't change this view for earth-conditions. So for more than two thousand years our view of Space didn't really change much in concept. Is it a wonder that Kant saw no movement, and spoke about 'a priori'? How should Kant have been able to observe that evolution is not linear, but accelerating. In his time basics on average changed once per 500 years, in the meantime around 3 times per century. It got 15 times faster.

In science we try to understand, and reason gives us metaphysics. Or science is modeling concepts, and metaphysics is pure reasoning. (Remark: luckily in Kant's view the models are given, because they would have taken a lot of reasoning or abstract thinking). So metaphysics is the product of pure reason and deals only with ideas in our head. Metaphysics according to Kant therefore is a mental activity, for instance DECIDING  whether or not God exists.

Physics simply describes the universe, and the laws of physics are only good for predicting what will happen. Metaphysics, by contrast, tries to explain the universe and why things happen the way they do. Metaphysicians do no experiments: they try to sort out everything in their HEADS (origin mind-body problem).

Metaphysics tries to find causal connections between events. Even if these are not noticeable by our senses. It is too easy to discredit metaphysics as not to be proven by traditional scientific methods. But it is also way too easy to think like Kant that abstract thought is innocent. He surely couldn't imagine yet the power of atom bombs.

Note that Kant lived long before Darwin and the resulting 'discovery' of DNA. This knowledge certainly would have influenced his ideas about 'a priori'. He would then have known that all creatures on earth are closely related because of evolution. Then the survival of the same concepts is not surprising, because of   'the survival of the fittest' (only a mistake in rationalism was to see fit as having power, while it is 'being successful').
What Kant tried to do can be seen as structuring mental thought given a temporary direction of evolution. Then his 'a priori' are the basic concepts during this stage of human evolution

Nevertheless the driving reason of Kant's thoughts is still up to date. He wanted to reconcile the empiricist and rationalist camps. This in the Western World in the meantime more or less happened. What however remained is an overdose of abstract thought as in rationalism.
It is in energy waste comparable to to energy slurping battle in the Muslim Paradigm between the Medina and Mekka Camps.

Newton thought that space is absolute, a thing in itself. Leibniz held to a relational theory of space, according to which space is a relational property that holds between objects. Space is not absolute, but dependent on the objects that are in it. Kant took neither side, both positions though share the assumption that space is mind-independent.

Kant posed that our concept of space is not something we learn from experience, but it a feature of our minds and not a feature of reality. Remark: Only this mind-feature can change and Kant's a priori intuitions were not supposed to change.

In fact Einstein's later  theory of relativity showed that the universe does not conform to the laws of Euclidean geometry. And that space and time are far more complicated than we until then thought. Space and time don't fit our experience anymore. That might have been a severe shock to Kant. But also a confirmation of his thought that 'space' is a concept. In Kant's model Einstein gave to the world partly a new set of a priori concepts. Einstein's ideas were an essential change of concepts ( Remark: this time a scientific paradigm shift).

Kant wrote about math: Now, the intuitions which pure mathematics lays at the foundation of all its cognitions and judgments which appear at once apodictic and necessary are Space and Time.

Math consists of synthetic a priori cognitions, we must be able to draw connections between different concepts by means of some sort of pure intuition. Kant uses for this phenomenon the word Anschauung, meaning literally a point of view or way of seeing (this is what Lakatos later called research fields, but is in fact using common sense expressed by individual experience).

So there must be some form of pure intuition (take care, here is meant a priori knowledge) within us that allows us to connect different concepts without reference to sense experience. Kant's answer is that space and time are actual not to be observed objects, but CONCEPTS in the dominant way of thinking.

Geometry is the a priori study of our pure intuition of space, and numbers come from the successive moments of our pure intuition of time. If space and time were things in themselves that we could only understand by reference to experience, geometry and math would not have the a priori certainty that makes them so reliable. (Remark: a priori knowledge could as well be the direction of evolution)

About a priori Kant writes: Therefore in one way only can my intuition [Anschauung] anticipate the actuality of the object, and be a cognition a priori. Remark nothing but the form of sensibility. And: I should be glad to know how it can be possible to know the constitution of things a priori

Nothing in space and time has one shape. Everybody perceives it in his/her own way. Beings with closely connected experience see something very similar. But who knows how a dolphin perceives a human?

(1) Geometry is the human way of perceiving space. Without this 3-dimensional insight we would be helpless beings. Kant explains our certainty by a priori knowledge and not from experience (his version of DNA).

(2) Idealism claims that there are no objects in the world, only minds, and that everything we see is just a construction of the mind. Kant argues that the things exist, and that they are the source of what we do perceive.

(3) Kant claims that every perception is a priori valid. Remark: Quite modern, people who deny Flying Saucers could learn from it.

What Kant refers to as "the science of nature" is what nowadays we would simply call "science". It is nothing more than a bunch of consistent dreams about evolution. Kant observes that we do indeed study natural science and make use of universal and necessary laws. Our behaviour shows regularity, but how is this possible?

Kant distinguishes judgments of perception and judgments of experience, or subjective concepts of empirical intuitions and concepts of understanding.

For instance a concept of empirical intuition is cause. I observe that a rock grows warm under the sun and judge that the sun caused the rock to grow warm. We do not find pure concepts of the understanding in experience. These concepts we only use to structure our understanding of experience. A priori concepts like this make sense of our perceptions. They are universally quite similar for humans, because these difference very little

Judgments of perception deal only with what we subjectively sense, or intuit, while judgments of experience objectively (given the concepts) deal with what we infer from our perceptions.

The table of judgments in section 21 is a trial of Kant to divide judgments into their logical parts quantity, quality, relation, and modality. For instance, the judgment "the sky is blue" is singular (it deals with the sky), affirmative (it affirms that the sky is blue), categorical (it is a simple subject-predicate sentence), and assertoric (it makes an assertion).

The following table of universal principles classifies the different kinds of law that correspond according to Kant with his concepts of the understanding.

UNIVERSAL PRINCIPLES OF THE SCIENCE OF NATURE.

• Axioms of Intuition.
• Anticipations of Perception.
• Analogies of Experience.
• Postulates of Empirical Thinking generally.

Hume believes habit makes us 'see' causality. In other word he believes in evolutionary causes of habits. Kant agrees that causality is just there, but he suggests, causation is an a priori concept of the understanding. See a priori as given, but that doesn't really imply that the can't be exchanged.  Kant is double in the possibility of changing such concepts, he shows belief in the human mind being constantly reshaping the world (relativism), but at the same time believes in rigid basic rules (absolutism).

Kant saw causation as a given concept and argues that we derive experience from such given pure concepts. Pure concepts and pure intuitions (given or not) shape our world, but they tell nothing about things in themselves.

First Part: Nature can be seen as totality of all our sensations by means of our pure intuitions of space and time.

Second Part: Nature can be seen as the totality of experience as understood and connected by laws, by means of our pure concepts of the understanding.

Thus, Kant concludes: "the understanding does not derive its laws (a priori) from, but prescribes them to, nature." Remark: only staying away from a priori intuitions

This can be seen as an arrogant view. But Kant doesn't deny that nature has limitless forms. Kant is juggling with concepts about concepts. A priori concepts are 'given' but nowhere he denies that different concepts can exist.

Early modern philosophy, from Descartes to Hume, is roughly divided between 'rationalists' like Descartes, Spinoza, and Leibniz and empiricists like Locke, Berkeley, and Hume. Rationalists emphasise pure reason. Empiricists stress knowledge gained from experience. Kant attempted a synthesis between these two camps, but at the same time attacked both sides.

Kant criticizes the empiricist view by pointing out that experience is already comes in an organized form. Here he kept to the idea that our experience of space and time is absolute, or in his words pure intuitions. But at the same time he thought that humans actively shape the world they perceive so as to make it intelligible. He restricted in this way active shaping to a world outside a priori concepts. But it showed his modern way  of thinking.

Rationalist argued that if synthetic a priori knowledge was possible, then one can learn substantial truths about the universe without experience. So reason outstands experience. Kant's answer is twofold. First, that our a priori pure intuitions and pure concepts learn us nothing about things themselves. Second, our pure intuitions and pure concepts do not give us any substantial knowledge. They are only recipees.

Metaphysics, as its name suggests, deals with matters that are beyond experience.

Any natural law that can be applied to experience belongs to the faculty of 'understanding' and has nothing is metaphysics. Reason only departs from experience.
Kant distinguishes three different kinds of "ideas of reason:
- psychological ideas
- cosmological ideas (next section)
- theological ideas (Critique of Pure Reason)

that structure all of physics. This summary will deal with psychological ideas. Psychological ideas try to identify Natural Laws underlying the descriptions. What is the cat after the description "a thing that purrs". Kant suggests that this search is futile: The only knowledge we can have comes in the form of predicates attached to subjects (very much like later Ludwig Wittgenstein worked out in his Investigations, this part of Kant's views never got much attention. Only Kant gave a unique central position to the fantasy 'spirit'.).

This fundamental fantasy is the invisible ghost animal 'thinking ego', or 'spirit'. Sayings like ("I think," or " I dream,") for example refer back to an "I" that is fundament for the hallucination of Immanuel Kant, is indivisible, and invisible. Kant argued that this "I" is neither a thing nor a concept (it is a 'spirit'). This conclusion suggested that Descartes was wrong in thinking we can know about the mind better than we can know about external bodies (because external bodies might be cut in parts for observation, and 'spirits' are indivisible and invisible).

The world according to Kant, presumes 4 claims of pure reason:

The world has a definite beginning and end (is finite)

All things are made up of simple, indestructible, indivisible parts.

We can act in accordance with our own free will.

Causes in some form are necessary.

Ad1) It makes no sense to ask whether or not the world has a limit in space and time, since that limit would exist outside the realm of our experience.

Ad2) Parts of things are only appearances, and so cannot have any existence until they are experienced.

Ad3) Freedom is an ability outside causality, and thus apart from experience. Freedom is therefore applicable only to things in themselves. We can be free and also be subject to the laws of nature.

Ad4) In the world of appearances, every causal connection may be contingent, which is to say it could have happened otherwise. Nonetheless, these appearances might have a necessary connection to things in themselves.

The highest value Kant attached to pure reason and called this the theological idea.

To this he dedicated his masterwork Critique of pure Reason.