What is the difference between "pliable" and "pliant"?

I am confused between pliable and pliant. What's the difference? The explanation in the Oxford Dictionary seems vague:

pliable

1. easily bent; flexible
   [quality leather is pliable and will not crack]
2. easily influenced
   [pliable teenage minds]

pliant

1. easily bent
   [pliant willow stems]
2. easily influenced or directed; yielding
   [a more pliant prime minister]

There isn't a difference in meaning; they're synonyms. They are also interchangeable as regards usage; wherever one fits, the other would too. Pliable is more common, though:

Pliable usually refers to a material flexing in response to an external force, while "plaint" can ALSO refer, allegorically, to other things (such as a personality) that exhibits flexibility in response to an external force.

I make a point of using "pliable" to refer to inanimate objects only, and "pliant" to intellectual/emotional states only. Purely an aesthetic choice, but individual use is a particle of language evolution.