Practicable, practical are not close synonyms and not interchangeable, but they are sometimes confused when they imply a capacity for being used or turned to account.
Practicable (see also POSSIBLE 1 ) applies chiefly to something immaterial (as a plan, project, scheme, or design) which has not been tested in practice or to something material (as a new machine, a new form of entertainment, or a new implement) which has not been proved successful in operation or use.
Practical applies not only to things both concrete and immaterial but also as practicable does not, to persons. The term in all of its senses stresses an opposition to what is theoretical, speculative, ideal, unrealistic, or imaginative and implies a relation to the actual life of man, his daily needs, or the conditions which must be met.
When the term also implies a capacity for use, it emphasizes actual usefulness rather than highly probable or merely discovered usableness; thus, a plan might be practicable in that it could be put into practice though not practical because inefficient, too costly, or superfluous; the modern low-slung high-speed automobile was practicable long before improved roads and fuels made it practical .
Hence, practical may apply to whatever is such in kind, character, amount, or effect that it is definitely useful or serviceable in actual life.