These words refer to things that can be moulded or bent. Malleable and ductile refer most specifically to the working of metals. Malleable indicates a metal, such as gold, that can be beaten easily into thin sheets or other forms at will. Ductile refers specifically to the ease with which a metal, such as copper, can be drawn out into a continuous wire; sometimes it can also refer to the readiness with which fluids will follow a given course. In this sense, water is more ductile than mercury. When these two words are used to describe responsive minds, malleable suggests an innocent or unformed character that easily takes an impression and can be decisively altered by the conscious attempts of another person or by propaganda: the age at which a normally malleable student is most open to influence, whether for good or ill. Ductile appears less commonly in this context; when it does, it suggests the capability of being subtly led towards a not always stated goal: a demagogue flattering his all too ductile audience.

Pliable and pliant are closely related. Used of physical objects, pliant often suggests something that resumes its shape after being bent: a pliant reed. Pliable is often used for something that will remain in any shape given to it: a pliable whip; pliable putty. When applied to character, consequently, pliable should suggest a greater openness to impression than pliant : half-truths purveyed to pliable minds; a readiness to learn that was pliant but not incredulous. Frequently, however, these words are used with no discernible difference in meanings.

Plastic most often refers to any substance that can be moulded and then hardened or set: plastic buttons; a plastic safety helmet. But he word can refer to any synthesized substance, however, treated, that is initially a liquid or gel: plastic shower curtains. Because of its overriding use in these cases, other uses of the word may be losing ground. Plastic can refer to an impressionable mind when it is still mouldable, unformed, or not yet fixed: the first years of life when the psyche is at its most plastic . The word can also refer to the creative impulse in general or to sculptural or three-dimensional qualities: the poet’s plastic ability to find new forms for new subject matter; a building considered strictly as a set of plastic values; the unique plastic designs of the choreographer’s ensemble work.