Most children find it very difficult to explain exactly what the words they use mean when those words do not refer to things that can be seen or touched. Yet, since children are able to use these words to convey the feelings and emotions they are obviously experiencing, understanding what a word means clearly does not depend on being able to explain it. Which one of the following principles, if accepted, would provide the most justification for the conclusion? ['Words can be explained satisfactorily only when they refer to things that can be seen or touched.', 'Anyone who can provide an exact explanation of a word has a clear understanding of what that word means.', 'When someone appropriately uses a word to convey something that he or she is experiencing, that person understands what that word means.', 'The fact that a task is very difficult for most people does not mean that no one can do it.']