Subjective Adjective (-ax)

I'm not sure why the suffix changes as it does. In the genitive case, the Latin suffix becomes “-acis”, which is pretty close, but I don't know why the genitive would be relevant. In any case, the letter “x” is short for “cs”, so the change isn't entirely far-fetched.

The subjective adjective doesn't just make a noun into the subject of a verb, it also specifies that the action is characteristic or habitual, or perhaps enjoyed. Or, as my Latin dictionary says under “-ax”,

implying tendency, ability

The present participle is also a subjective adjective, but with a different meaning—it specifies that the action is currently being performed.

Here are some more examples of subjective adjectives.

audeo	I dare	audax	audacious
teneo	I hold	tenax	tenacious
rapio	I seize	rapax	rapacious
efficio	I produce	efficax	efficacious
edo	I eat	edax	edacious (?)
voro	I devour	vorax	voracious

I'm just kidding about “edacious” … it could be a word, but isn't. But, speaking of “edax”, here's the start of a poem by Horace that I like a lot. I learned it from my Latin book.

Exegi monumentum aere perennius
regalique situ Pyramidum altius,
quod non imber edax, non Aquilo impotens
possit diruere aut innumerabilis
annorum series et fuga temporum.

It strikes me as a kind of opposite to Ozymandias.

The phrase “characteristic or habitual” that I used above to describe the subjective adjective I also used earlier to describe the subjective noun. I don't think the two are grammatically related, but they really do seem to have the same meaning—a fact that we can actually check, as follows.

Nouns in Latin can often be made into adjectives via the suffix “-ius”. If we do that to the subjective noun “praedator”, we get the adjective “praedatorius”; dropping the suffix “-us”, we obtain the corresponding English word, “predatory”; and that, indeed, is a synonym of the subjective adjective, “predacious”.

Speaking of predators, I'm reminded of a running joke from my high-school German class. We must have read some passage that referred to a Raubvogel, a bird of prey; for months afterward, we looked for any excuse to mention the dreaded Raubfisch, the “fish of prey”. That might even be a real word!

Finally, speaking of converting nouns into adjectives, or rather vice versa, here's something else that's relevant to subjective adjectives.

Adjectives in Latin can be used as nouns, but they can often also be converted into nouns via the suffix “-itas”. The word “verus”, “true”, for example, becomes “veritas”, “truth”; and the subjective adjective “capax”, “capacious”, becomes “capacitas”, “capacity”. Most English words ending in “-acity” are derived from subjective adjectives.

There are some Latin adjectives that follow the same pattern as the subjective adjective, but with different vowels. “Ferox”, “fierce”, for example, leads to “ferocious” and “ferocity”; “felix”, “happy”, to “felicity”. I suspect these are derived from verbs, but I wouldn't swear to it. The only one I'm sure about is “velox”, “fast”, which leads to “velocity”—it is derived from the verb “velo”, “I cover (veil)” … or, in this context, “I put up sails”.

Of course, we mustn't forget the equally-dreaded potatoes of prey.