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FUTURE LOGIC©
Avi Sion, 1990 (Rev. ed. 1996) All rights reserved.
14.
MODAL OPPOSITIONS AND EDUCTIONS.
We have already encountered the oppositions of actuals or momentaries in
classical logic. There is subalternation from A
to R, to I; and from E to G,
to O. A and E,
A and G,
R and E, are pairs of
contraries; A and O,
I and E,
R and G, are pairs of
contradictories, R and O,
I and G,
I and O, are pairs of
subcontraries. These relationships were shown to proceed from analysis of the
forms' meanings and application of the laws of thought. In the wider context of
modal logic, we are concerned with the oppositions of, not only these six forms,
but 24 more.
Remember that subalternation is one-way implication, contradictories can
neither be both true nor both false, contraries cannot be both true but may be
both false, subcontraries may be both true but cannot be both false, and
unconnecteds do not affect each others' truth or falsehood.
1.
Quantification of Oppositions. 2.
Basic Intramodal Oppositions. 3.
Quantified Intramodal Oppositions.
1.
Quantification of Oppositions.
At this point, I would like show how, given a certain oppositional
relation to exist between two singular propositions (s1,
s2), referring to the same instance
of the same subject-concept, we can systematically predict the oppositions
involving one or two of the corresponding universal (u1, u2) and particular (p1,
p2) forms. This doctrine may be called quantification of
oppositions, meaning more precisely opposition of quantified forms. It allows us
to introduce quantity into basic figures of opposition, such as that between the
categories or types of modality which will presented in the next sections.
Consider the following general-model figure of opposition. Diagram
14.1 Quantification of Oppositions.
Grant that we already know the subalternations, labeled (1), to be true,
since universality includes singularity, which includes particularity. For any
given opposition between singulars, labeled (2) horizontal, we need to discover
the remaining lines of oppositions, namely (2) diagonal, (3), and (4). The
following results are obtained.
If the singulars are implicants,
then all horizontal lines signify implicance, and all diagonals signify
subalternation, downward. Proof for the horizontals: since it is given any pair
of singular forms s1, s2 mutually imply each other, then any full or partial enumeration
of such pairs, as in u1, u2,
or p1, p2, will likewise
mutually imply each other, provided the extensions involved are the same. For
the diagonals: since u1 implies s1,
and s1 implies s2, then u1
implies s2. Since u1, s1,
imply s2, and s2 implies p2,
then they also imply p2. Likewise, u2, s2 can be shown to
imply s1, p1.
If the singulars are subalternative,
left implying right, then all horizontal or left down to right diagonals signify
subalternation in that direction, and all right down to left diagonals signify
unconnectedness. Proof: similar to previous case, though the relations involved
here are unidirectional. Unconnectedness, of course, applies when no more finite
opposition can be established.
If the singulars are contradictory,
then all lines labeled (2) signify contradiction, all lines labeled (3)
contrariety, all lines labeled (4) subcontrariety. Proof for the upper square:
given that s1 and s2 cannot both be
true, then any enumerations which include them both, such as u1
+ s2, s1 + u2,
or u1 + u2, cannot be both
true (so, for instance, if u1=T, then
u2=F; i.e. if u1, then not-u2). Proof
for the lower square: given that s1
and s2 cannot both be false, then any
enumerations which exclude them both such as not-p1 + not-s2, not-s1
+ not-p2, or not-p1 + not-p2,
cannot both be true (so, for instance, if not-p1
= true, then not-p2 = false; i.e. if
not-p1, then p2). So far, we have proven the claimed contrarieties and
subcontrarieties. But what of the contradictions of u1 + p2, or p1
+ u2? If we affirm such a pair, we do not necessarily thereby affirm a
specific s1 + s2 pair true, but we do imply that some unspecified pair(s) of s1
and s2, referring to one and the same individual, would be posited
together; this shows the incompatibility of u1 + p2, or p1
+ u2. Likewise, for the incompatibility of not-u1 + not-p2, or not-p1
+ not-u2, there is bound to be some unspecified case(s) of not-s1
+ not-s2 subsumed, against our given information.
If the singulars are contrary,
then all lines labeled (2) or (3) signify contrariety, and all lines labeled (4)
unconnectedness. Proof: see the relevant ('not both true') parts of the
arguments above for contradiction.
If the singulars are subcontrary,
then all lines labeled (2) or (4) signify subcontrariety, and all lines labeled
(3) unconnectedness. Proof: see the relevant ('not both false') parts of the
arguments above for contradiction.
These general rules of opposition can now be used in any context, saving
us from having to deal with each case of quantification anew. 2.
Basic Intramodal Oppositions.
The following diagram concerns singular propositions only, and is
designed to illustrate the relationships of the different categories of
modality, whether of the natural type or of the temporal type (each type
separately). Diagram
14.2 Oppositions
of Main Categories of Modality.
The above is equivalent to the figure of oppositions of the six
quantities of Aristotelian propositions, and may be established by similar
argument. The vertical, downward subalternations proceed from the definitions of
the concepts involved; 'all' the circumstances or times includes any 'this one'
we pick, and any specific 'this one' implies 'some' unspecified number.
The horizontal contradiction is simply the axiomatic presence and absence
incompatibility. The diagonal contradictions between necessity and unnecessity,
or impossibility and possibility, follow, on the basis that there would
otherwise be individual circumstance(s) or time(s) which contained both presence
and absence, or neither.
For the rest, the proofs are very mechanical consequences of the above.
For example, using the symbols n, a,
p, with subscripts +
and -, we can say: n+ implies
a+ implies not{a-},
whereas not{n+} does not imply not{a+},
nor therefore a-, so that n+
and a- are contrary; or again, not{p+}
implies not{a+} implies a-,
whereas p+ does not imply a+, nor
therefore not{a-}, so that p+
and a- are subcontraries.
With regard to contingency; being defined as the sum of possibility and
unnecessity, it subalternates p+ and p-, and is contrary to n+
and n-. Incontingency, its negation,
therefore means either necessity or impossibility, and is subalternated by n+
and n-, and subcontrary to p+
and p-. Contingency and incontingency
are both oppositionally unconnected to presence and absence. These relationships
could be represented in a wedge-shaped diagram. As for the oppositions of probability forms, see remarks in Appendix 2.
We can view necessity as the highest form of probability. Also,
probability, whether high or low, is merely a more defined form of possibility.
If we express a more specific proportion of cases (e.g. 75% or 33%), we obtain
sub-categories of probability. Lastly, of course, none of the probability forms
are connected oppositionally to the presence/absence forms. Nevertheless, the
whole idea of probability thinking is to try and predict the chances of
realization of presence or absence. 3.
Quantified Intramodal Oppositions.
If we take each of the oppositional relations between singulars of
natural modality and quantify them with the general rules, we obtain the
following table of opposition for all the forms of natural modality.
Table
14.1 Table
of Oppositions in Natural Modality.
These relationships may be clarified by use of a truth-table. In the
table below, given the truth of a proposition listed under column heading T,
or the falsehood of one under F, we
see the reactions, along the same row, of all other propositions, listed as
column headings. This data follows from the preceding table.
Table
14.2 Truth-Table
for Natural Modality. (key: T = true, F = false, . = undetermined.)
Needless
to say, the easiest way to visualize and transmit all the above information is
by means of a figure of opposition. However, since in this context the required
diagram is three-dimensional, it is rather difficult to present on paper. Below
is a sketch of it, but without the various lines of opposition. Note that the
shaded planes have already been presented earlier, with all their lines of
opposition shown. The reader can work out the remaining planes, with reference
to the above two tables, or more radically to the principles of 'quantification
of oppositions' developed earlier. Diagram
14.3 Figure of
Oppositions of Natural Propositions.
Identical results are obtainable for temporal modality, substituting c
for n, and t for p, throughout.
Lastly, needing elucidation, is the inter-opposition of natural and
temporal modalities. The following diagram shows the continuum of modality,
including both natural and temporal types together. Parts of this diagram have
already been presented, when we dealt with each modal type separately. But it is
interesting to have an overview, anyway. Diagram
14.4 Oppositions
between Modality Types.
This diagram concerns singulars. We know from our analysis of modality
that n implies c,
which implies a or m, which implies t, which
implies p, for either polarity; that
is, the illustrated subalternations proceed from the meanings of the concepts
involved. From these, and the already established intramodal oppositions, it is
easy to infer the contrariety between n and c, or n
and t, forms of opposite polarity (upper diagonals), and the
subcontrariety between c and p,
or t and p, forms of
opposite polarity (lower diagonals).
These relationships between singulars can now be quantified by reference
to the general rules of opposition, and the results tabulated as follows.
Table
14.3 Table
of Oppositions between Natural and Temporal Modalities.
These relationships may be clarified by use of a truth-table. This data
follows from the preceding table.
Table 14.4
Truth-Table for Intermodal Oppositions. (key: T = true, F = false, . = undetermined.)
In the table above, given the truth of a proposition listed under column
heading T, or the falsehood of one under F, we see the reactions, along the same
row, of all other propositions, listed as column headings.
The following is a list of the eductions possible from propositions with
natural modality. The methods of validation used for these are similar to those
developed for Aristotelean forms. That is, conceptual analyses and appeal to the
laws of thought, in the cases of obversion and conversion; and reduction to
these first two process, in the other cases.
a.
Obversion
(S-P to S-nonP).
S must be P implies S cannot be nonP; S cannot be P implies S must be
nonP; S can be P implies S can not-be nonP; S can not-be P implies S can be
nonP. These are true irrespective of the quantity (all/this/ some) involved; and
the obverse has in all cases the same quantity as the obvertend. These results
follow from the definitions of the concepts involved and the law of
contradiction.
b.
Conversion
(S-P to P-S).
Affirmatives, be they necessary or potential, general or particular, all
convert to a particular potential, Some P can be S, but no better. In the case
of negatives, only No S can be P (En)
is convertible, and that fully to No P can be S; Ep,
Gn, Gp, On, Op
are not convertible. These results can be established by consideration of the
subsumptions of circumstance involved.
c.
Obverted
Conversion (S-P to P-nonS).
This process is applicable only to convertibles, which are then all
obvertible. Thus, affirmatives all yield Some P can not-be nonS; and En
yields All P must be nonS.
d.
Conversion
by Negation (S-P to nonP-S).
This is obversion, followed by conversion. Thus, all originally negative
propositions can be converted by negation, to yield Some nonP can be S. But of
originally affirmative propositions, only All S must be P (An)
can be so processed, to yield No nonP can be S; Ap, Rn, Rp,
In, Ip are not
convertible by negation.
e.
Contraposition
(S-P to nonP-nonS).
This requires conversion by negation, followed by obversion. Therefore,
all negatives are contraposable, and that to Some nonP can not-be nonS. Whereas,
in the case of affirmatives, only An
can be so processed, yielding All nonP must be nonS.
f.
Inversion
(S-P to nonS-nonP).
Of affirmatives, only An can
be so treated, by contraposing then converting it, to obtain Some nonS can be
nonP. Of negatives, only En is
invertible, by converting then contraposing it, with the result Some nonS can
not-be nonP.
g.
Obverted
Inversion (S-P to nonS-P).
This being inversion followed by obversion is applicable only to
universal necessaries, An yielding Some nonS can not-be P, and En yielding Some nonS can be P.
We note, in conclusion, that only An
and En (as well as A and E)
can be subjected to all six of these processes.
Similar results can easily be established regarding propositions with
temporal modality.
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