Modality is that aspect of our
reasoning and/or speech that employs the services of ‘possibility’ and
‘necessity’, and henceforth we shall know ‘possibility’ and ‘necessity’ as
‘modal operators’. There are four senses in which we use the modal operators.
First, when we want to express modal statements of time, for instance, when we
say “it was the case that so and so” or “it will be the case that so and so”.
This type of modal expression in philosophical jargon, is referred to as
temporal modal statements. Second, when we express modal statements of believe,
for instance, when we say “I believe that so and so” or “I believe that
whatever happens, so and so will be the case”. This is referred to as doxastic
modal statements. Third, when we express modal statements of duty, for instance,
when we say “it is permissible that so and so” or “it is obligatory that so and
so”. This is referred to as deontic modal statements. Fourth, when we express
modal statements of knowledge, for instance, when we say “I know that so and
so” or “I know that so and so come what may”. This is referred to epistemic
modal statements. I gave two examples each for the four senses to demonstrate
how the modal operators are implied when we make such expressions. The first
set of examples implies the possibility sense, while the second implies the
necessity sense. I hope I have not projected the idea that only in philosophy
is modality useful. Modality is ubiquitous in everyday living and in science
also.
When we say that the eggs are
fragile, we are not stating what is happening at the moment of utterance to the
eggs in our kitchens, rather we are stating what could happen to the eggs if
exposed to such and such conditions. Other everyday statements that are
essentially modal in character include; I am unable to speak German, Joe could
win the chess in three different ways, you cannot break the law of physics. In
all of these examples, we are saying something that goes beyond what is
strictly the case. Apart from the pervasiveness of modality in our everyday
reasoning, science normally ascribes dispositional properties to various
objects. Salts might not readily be soluble, hydrogen is flammable, and uranium
has the tendency to decay, and so on. These are facts about the object’s
tendencies or capacities; they are not about what is actually happening to the
object. They are in simple terms, modal facts. You probably are wondering what
all of these has got to do with sophisticated philosophizing and your wondering
would not have been misplaced.
Sometimes in the future, I will take you back to the history of the
development and transition of philosophy from one era into another; but for
now, it suffices to say that philosophy thrives on conceptual clarification. This
has made some philosophers think logic and philosophy of language are a little bit
more important than all other aspects of philosophy. What I think is not
important and whether you agree or disagree, it does not remove the fact that
most of the problems with our explanations of phenomena is lack of precision
and clarity. Thus it was that every aspect of our reasoning was formalized
logically so as to install this precision and clarity. I am talking about the
kind of simple formula that when followed, what we intend to say is as clear as
day. I make one simple example.
P ⊃ Q If
P, then Q
P P
∴ Q Therefore
Q
This is one of the formula in propositional
logic, and it is called ‘material implication’. Don’t fret for now about the
meaning of these technical terms, they will become clearer when I talk about
logic sometimes in the future. Now, consider this everyday reasoning and see
how its truthfulness is guaranteed by the rule of material implication. “If it
is a human being, then it has at least one parent”. It is a human being, and so
we conclude that it has at least one parent. There is no instance of
argumentation that can be wrong if we abide by formal rules of this sort. Consequently,
with rules like this, we can make precise and clear what we intend to say; our
arguments and analyses of phenomena becomes clearer. However, modal statements do
not follow these logical rules.
Take for instance another
everyday statement “If the ground is wet, then it must have rained”. This
statement is clearly like the first one used to explain the material
implication rule. Its truthfulness should also be guaranteed by the material
implication rule, but that is not the case. Suppose the ground is wet, it would
be mistaken to conclude that it definitely had rained. This is not because the
ground would not be wet if it had rained, but because the statement employs the
service of the necessity operator. It is a statement of necessity, and it is
not a matter of necessity that the ground is wet only when it rained. This is
the kind of trouble modality caused logicians and philosophers of language. It
suffices to say that no one knew what to do with modal statements until Stig
Kanger in 1957 came along. He was the first to notice that modality is so
entrenched in our life that it makes all efforts so far in logic and philosophy
as a whole, seem little if something tangible in formal logic is not done about
modality. He showed through a formal system that we can prove the truthfulness
of a modal statement. When I say ‘formal system’, the kind of elegant
quasi-mathematical formula above should come to mind. Shortly after Kanger in
the same year, Jaako Hintikka came along with a formal system of deontic logic
and as you would recall, deontic is one of the senses in which we use modal
statements. However, it was not until Saul Kripke some few years after Kanger
and Hintikka, in 1959, that a completeness theorem for modal logic was proved.
A formal system is complete when every consistent statement that can be formed
using the system is derivable from the system. It might be reasonable to talk
about the magnitude of what Kripke achieved, but I reserve that for the time I
talk about logic.
In 1970, Kripke carved out an
ever-increasing chasm between what we know to be possible or necessary on one
hand and what is possible or necessary on the other. The former has come to be
known as epistemic modality and the latter as metaphysical modality. I will
start with the latter and from there move unto the former, but I should warn
you; we might spend weeks on just the latter, so do not expect a quick survey.
I intend to publish a post once every week. Since this is my first ever post, I
hope I have not disappointed. I intend to speak in clear language and use
technical terms as scarcely as I can; philosophy is grey enough because the
common man thinks philosophers speak and use terms that no one except
themselves understand. I do not intend to encourage such (mis)understanding
hence my desire to speak in clear language. I also intend to make the posts as
short as possible; somewhere between 1000 to 1500 words. Whatever I mention and
simply pass over which you think deserves more attention than I have given it
will be dwelt on more in the comment section and if you prefer, I privately
inbox you. I do not presume to know all on any given topic and whatever I post
here is subject to corrections and updates. My intent and why I started this
blog to reiterate, is to bring philosophy to the foot of everyone except the
philosopher’s. I hope to remove the ewwww‼!
attitude philosophy gets by explaining what it is philosophers do and why
it is important that they do so, if at all it is important. At the end of every
post, I will add a list of references for the curious minds. Once you notice I
am breaking any of these promises, please do caution me and bring me back to
base. Next week, I begin with metaphysical modality. I hope you have had a
fruitful reading.
Kripke,
S. (1959). A Completeness Theorem in Modal Logic. The Journal of Symbolic Logic Vol. 24, pp. 1–14.
Kanger, S. (1957). Provability in Logic. Almqvist and
Wiksell.
Hintikka, J. (1957). Quantifiers
in Deontic Logic. Societas Scientiarum
Fennica, Commenationes Humanarum Litterarum 23 No. 4.
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