I'm sure this is a useless question, but it has been bothering me
since it occurred to me. Why is it we travel ''on'' a bus, ''on'' a
train, ''on'' a boat, ''on'' a plane, but ''in'' a car? As we also
travel ''in'' cabs and police cruisers, it begs to reason that it
has less to do with ownership of the vehicle and more to do with
the size of the vehicle.
Nevertheless, the original models for automobiles weren't
enclosed, to it seems likely that the usage would have favored
''on,'' since the riders were not ''in'' anything.
The best reason I can think of is that the usage transferred from
the horse-drawn carriage, which some of us still ride ''in'' today,
but that only cycles the question further back.
Bearing in mind that the modes of transportation at that point
would have been the boat, the carriage, forms of animal
(primarily horse), and later on the train, it makes sense to be
''on'' a boat and ''on'' a horse, but ''in'' a carriage. But why ''on''
This, however, pushes the question forward yet again -- why,
then, do we not ride ''in'' a plane or ''in'' a bus?
As my colleagues have pointed out, English prepositions are not consistent in their
uses. However, there are very common and well-known basic locative senses for
several of the prepositions you mention.
These senses are discussed and explicated, along with much else, in Charles
Fillmore's Santa Cruz
Deixis Lectures, particularly Lecture 2, "Space".
From that lecture:
"In particular, the preposition at is said to ascribe no particular
dimensionality to the referent of its assiciated noun, the preposition on is
said to ascribe to the referent of its head noun the property of being a line or a
surface, and the preposition in is said to ascribe to the referent of its head
noun the notion of a bounded two dimensional or three-dimensional space.
"Frequently the same noun has different interpretations depending on what
dimensionality property is assigned it by the accompanying preposition [e.g.]
"at the corner, which means near or in contact with the
intersection or meeting of two straight lines -- or two streets
"on the corner, which locates something as being in
contact with a particular part of the surface of some angular two-dimensional figure
or three-dimensional object; while
"in the corner is an expression in which the noun
corner is used to indicate a portion of a three-dimensional space -- in
particular, a part of the interior of say, a room."
As far as vehicles are concerned, one is on a raft or a road or a scheduled
conveyance (rafts, roads, and schedules are all 2-dimensional), and on a horse as
well, because the back of a horse is 2-dimensional. One is, however, in a
boat or a canoe or an auto or a bus or a railway car (basically, any container,
because containers are 3-dimensional).
For scheduled conveyances, in the bus means physically inside
the conveyance, while on the bus means scheduled as a
passenger and/or physically present as well.
There's lots more, but you can get it in the links.