It's amusing how a simple typo can send you scurrying for the OED. In a post about the intellectual history of the Enlightenment, Diana Hsieh writes of the "philosophical cannon". Now there's a concept! The OED notes that "the spellings canon and cannon occur side by side down nearly to 1800, though the latter is the more frequent after circa 1660". Both 'canon' and 'cannon' derive ultimately from the Greek καννα meaning "a reed". Yet the terms diverged early on, with κανων meaning "a straight [and presumably solid] rod" as well as "a rule" used by carpenters, whereas 'cannon' derives from the hollow side of the reed/rod family (Italian cannone is a large tube or barrel). Nietzsche once claimed to be philosophizing with a hammer, but to philosophize with a cannon is really to bring out the big guns!
That line from Nietzsche is often interpreted in a nihilistic sense, with "hammer" understood to be a sledgehammer (something one step short of a philosophical cannon, as it were). Yet the full quote from the preface to Twilight of the Idols reveals a lighter touch:
This essay too -- the title betrays it -- is above all a recreation, a spot of sunshine, a leap sideways into the idleness of a psychologist. Perhaps a new war, too? And are new idols sounded out? This essay is a great declaration of war; and regarding the sounding out of idols, this time they are not just idols of the age, but eternal idols, which are here touched with a hammer as with a tuning fork: there are altogether no older, no more convinced, no more puffed-up idols -- and none more hollow.
Nietzsche's talk about idols hearkens back to Francis Bacon and his discussion of the Four Idols in The New Organon (an οργανον is a man-made tool, which is why our current sense of "organic" is diametrically opposite from the term's root meaning!). Interestingly, the English meaning of idol as the image of a false god (extended by Bacon to mean a dogma) was the final sense of the Greek ειδολων to develop historically -- the term originally meant an appearance or phantom, later on an image (as in a mirror), then a mental image or idea (as in Plato's "Theory of Ideas"), then a mimetic likeness as in a statue or "graven image". In English we retain the same root notion of vacuity in the word "idle".
And a dogma is just idle words: it is what one believes or holds to be true ('tenet' comes from the Latin tenere meaning "to hold") -- usually a philosophical belief, and not always one that is justified (for Bacon a philosophical dogma was prima facie suspect, since it was not derived from nature but from the self-spun web of human ideas and language). Because karma is a Sanskrit term that means "action", when we say "my karma ran over my dogma" we essentially mean that actions speak louder than words. Tenets, anyone?