Definition of
   a priori






Reasoning /inference/ starts from one or several premises and terminates hopefully in at least one conclusion.

When reasoning combines increasing number of credible premises, the conclusion becomes increasingly credible.


Rationalists and Scepticists both appreciate reasoning in the same manner. They share the same opinions about how logically correct argumentation leads from premises to conclusions.

The difference is formed about what should be regarded as credible ultimate premises for the arguments.


Premises are formed through perception


A premise, or starting point, of an argument is ultimately formed through perception, from a memory (that also is based on perception), or from memories of conclusions from previous arguments.

These previous arguments originate from previous premises that, as above, may be conclusions from earlier arguments. These also originate from premises... and so forth.

After searching in the chain of previous arguments we find that the initial premises (which in antique philosophy were called "primitives") are always formed through perception.

This is not a novelty:

Thus from perception there comes memory ... and from memory ... experience ... .
And from experience ... there comes a principle of skill or of understanding ... .

Thus it is clear that it is necessary for us to become familiar with the primitives by induction; for perception too instils the universal in this way.

Aristotle - Posterior Analytics 2, 100a5.

a priori and dogmas as premises

The claim that the premises always ultimately are formed through perception is opposed to rationalist's propositions that premises may consist of concepts that they claim to be "absolutely certain" which is discussed at the page a priori.

Also dogmas are ultimately based on perception, in spite of them being impossible to verify.

For instance the fantasy concept "unicorn" is understandable because it is formed through synthesis of concepts based on e.g. lion, horse and rhinoceros

In case an expressed sound, e.g. "sekruiipam", would not ultimately be based on perception, it would become completely unintelligible because it cannot be associated with anything in our experience.

Synthesis of the concept unicorn

Synthesis and analysis


Reasoning implies that propositions are combined or separated in processes that are called synthesis and analysis, respectively.

Generation out of the elements is /…/ synthesis, and generation into the elements is analysis

Aristotle, On the Heavens ii, §5, 303b13.

... ratiocination; which consists ... in composition, and division or resolution.

And the resolutive is commonly called analytical method, as the compositive is called synthetical.

Hobbes T - On Body (De Corpore) 1.6.1 (English Works vol.01, Molesworth, Bohn 1839, p.66).

All animals, including humans, use swift and often unconscious synthesis and analysis during perception and reasoning. Maybe this also is applicable for insects.


Synthesis implies coupling of related premises to concepts. The conclusion of the synthesis becomes more composite than its premises. When we possess several related concepts they may be synthesized and analysed to abstractions, i.e. to abstracted concepts.

Analysis implies use or application of one or several parts of a composite concept. We hence substitute a concept with a part of its content. The conclusion(s) of the analysis becomes less composite than its premise.

Because the premises of reasoning are ultimately based on perception, both synthesis and analysis lead to probability arguments.