The eight fundamental rules of the syllogism

Laurent Georget
4 min readJul 10, 2023


1) that there are three terms: the “Big”, the “Medium” and the “Small”… The Middle Term is the one common in both affirmations. Thus in the famous classical syllogism:

— All men are mortal,

— But Socrates is a man,

— So Socrates is mortal,

The term “man” is the “Middle Term” (M), “Socrates” is the “small term” (t), “mortal” is the large Term (T)

-2) That the large term and the small term do not have a greater extension in the conclusion than in the premises. Thus in the previous example: the term “mortal” (T) and the term “Socrates” (t) which make up the conclusion Socrates is mortal, are both in the “singular” in the sentence, they express a “particular” case (and not a general case), so they don’t have a greater “extension” in the conclusion than in the premises…

-3) that the conclusion does not contain the middle term. In the previous example, the conclusion “therefore Socrates is mortal”, no longer brings up the middle term (man), this only serves to achieve the fusion of the premises, which is why it disappears, as soon as the we formulate the conclusion.

-4) that the medium term be taken at least once in its entire extension. In the previous example the term man includes

all men, it is taken in its maximum extension which extends to all humanity.

-5) two affirmative premises cannot lead to negative conclusions (this is obvious)

-6) of two negative premises, nothing follows (idem)

-7) the conclusion always follows the weakest premise (the conclusion must necessarily be a negation, if one of the premises is, the conclusion must be particular, if one of the premises is)

-8) of two particular Premises nothing follows. One of the premises must imperatively establish a relationship whose scope is universal, as in “every man is mortal” (cf. rule number 4)

This is so because the fundamental process of reasoning is that of “deduction” : reasoning only works because it is “deductive”, which means that the conclusion must imperatively be included (or contained) in the Premises, this is why it is necessary that, on the one hand, at least one of the Premises states a “general law”, and on the other hand that the “middle term” is taken at least once in all its extension , in order to contain “in them” the conclusion, and this is what rules 4 and 8 express.

A reasoning therefore progresses from the “general” to the “specific”, it consists in deducing from a general law a particular application.

For example from the general law “every man is mortal”, we deduce “Socrates is mortal”, because Socrates is indeed included in “every man”.

  • The cognitive act which proceeds from the general to the particular characterizes “reasoning”: it is “deductive” ;
  • The cognitive act which proceeds from the opposite, and which goes from “particular to general”, characterizes induction.

“Deduction” and “induction” are thus two inverse cognitive movements :

— The first is “discursive” : by deduction, it extracts a particular application from a general law;

— the second is “intuitive” : by induction, it grasps the universal necessity of a particular fact, in order to formulate a general law.

The six complementary rules

The eight fundamental rules set out above are supplemented by six others, just as necessary to guarantee the truth of a reasoning.

Thus, for reasoning to infallibly generate a conclusion whose truth is assured and guaranteed in advance , not only must the eight rules governing the formal structure be rigorously respected (see above), but it is also imperative that the six following conditions,

concerning the Premises

are strictly checked.

For the truth of the conclusion of a reasoning to be guaranteed, it is essential:

-1) that each of the premises be “true”, that is to say absolutely consistent with reality. Let us recall here that a judgment is “true” as soon as the attribute which is affirmed to belong to the “grammatical subject” does belong to it in fact in concrete reality, hence the

need to always verify the value of an affirmation, in confronting it with concrete reality (through experience and empirical observation) !

-2) that each of the premises is strictly reducible to “first judgments”, which can be “judgments of existence”, or else

“definitions” directly resulting from immediate experience, or else “general laws” ( axioms) directly acquired by induction.

-3) that each of the premises be “immediate”, that is to say instantly verifiable by concrete experience or reducible to a previous concrete experience … In other words, each of the premises must be acquired by an act of intuitive (sensory) intellection , abstractive or inductive), which generate knowledge that is always infallible in their order, provided that the subject-knower remains sufficiently attentive to what he wants to judge and know.

-4) that the premises are prior to the conclusion ; this is obvious since a reasoning being of a deductive nature, the premises must be known beforehand.

-5) that the Premises are better known than the conclusion ; this again is obvious, and for the same reasons as above.

-6) that the Premisses are the cause of the conclusion ; in this respect, all of what has been developed previously explains and fully justifies this last condition.



Laurent Georget

Born in France and living in China since 2007. I am a certified Integral and Transpersonal Coach, supporting people in their personal development.