Austin, Aristotle, and Philoponus on things that glow in the dark

gistfile1.tex

The primary object of sight is the visible. What is visible is
either color or ``a certain kind of object which can be described
in words but which has no single name'' (\emph{De Anima} \textsc{ii}.7
418\( ^{b} \)4). So color is \emph{a} primary object of sight not
\emph{the} primary object of sight. That a sense can have a plurality
of primary objects is consistent with Aristotle's two defining
conditions on being a primary object---that it be perceptible to
one sense alone and about whose presence no error is possible.
Distinct kinds of objects can each satisfy these conditions. So it
does not follow from Aristotle's definition of primary objects that
for each sense there is exactly one primary object. If there is a
problem, especially if, as in the case of touch, there are too many
primary objects, this must be due not soley to the definition of
primary object but must involve as well further explanatory
assumptions.

Colors depend upon light for their visibility. But not everything
that is visible depends upon light for their visibility. That which
has no common name does not depend upon light for their visibility:
\begin{quote}
	Some objects of sight which in light are invisible, in
	darkness stimulate the sense; that is, things that appear
	fiery or shining. This class of objects has no simple common
	name, but instances of it are fungi, horns, heads, scales,
	and eyes of fish. In none of these is what is seen their
	own proper colour. Why we see these at all is another
	question. (\emph{De Anima} \textsc{ii}.7 419\( ^{a} \)xx--xx)
\end{quote} Philoponus, in his commentary on \emph{De Anima}, reports
a slightly different list of examples: \begin{quote}
	\ldots\ glow worms, heads of fish, fish scales, eyes of
	hedgehogs, shells of sea-creatures, which things are seen
	not in light but in dark. (\emph{On \emph{De Anima}} 319
	25--27; \citealt[3]{Charlton:2005fk})
\end{quote} That which has no common name possess qualities visible
in the dark and not the light and differ from the proper colors of
these same things which are visible in the light and not the dark.
This is most likely the source of Austin's example from \emph{Sense
and Sensibilia} (an appropriately Aristotelian title, at least in
the present context): \begin{quote}
	Suppose \ldots\ that there is a species of fish which looks
	vividly multi-coloured, slightly glowing perhaps, at a depth
	of a thousand feet. I ask you what its real colour is. So
	you catch a specimen and lay it out on deck, making sure
	the condution of the light is just about normal, and you
	find that it looks a muddy sort of greyish white. Well, is
	\emph{that} its real colour? \citep[lecture \textsc{vii},
	65--66]{Austin:1962lr}
\end{quote} In the darkness, at the depth of a thousand feet, the
fish may look vividly multi-colored and slightly glowing, but on
the sun drenched deck they look a muddy sort of greyish white.
Aristotle would contend that only the latter is the creature's
proper color. Austin is, of course, making a different point with
the Aristotelian example, that the `real' color of a thing may
depend on the practical point of attributing color to it in the
circumstances of saying.

There is a question about how broadly the domain of that which has
no common name extends. Some commentators have suggested that shining
be interepreted as reflective highlights. So fish scales, having a
highly reflective surface, can produce highlights discernable even
in conditions of very low illumination resulting in a shimmering
effect amidst the surrounding darkness. The trouble with this
interpretation is that it does not fit all of Aristotle's
examples---fungii lack smooth, reflective surfaces and so give rise
to no reflective highlights. One plausible thought, supported by
Philoponus' additional example of glow worms, and exploited by
Austin in his appropriation, is that these are examples of
bioluminescence. One minor problem with this interpretation is that
the eyes of hedgehogs (assuming, for the moment, that Philoponus'
example is of genuine Aristotelian province), glowing in a dark
field, are not radiant light sources the way that they appear to
be and the way that cases of  bioluminesecence genuinely are. Rather,
they are reflecting ambient light in circumstances of low illumination,
from a lantern of shaved horn, say, held by an anceint perceiver
traversing the field at night. All of Aristotle's examples are
biological, but the claim that that which has no common name is
visible in the absence of light suggests a generalization. After
all, there are mineral deposits whose glow can only be seen in the
absence of competing illumination. So perhaps that which has no
common name includes not only the bioluminescent, but the luminous
more generally. Philoponus suggests this broader interpretation and
provides the nice example of starlight, visible only in the absence
of the sun's light (\emph{On \emph{De Anima}} 347 11).