If one names the radio-active substances _elements_, one is placing in this class substances which are specially characterised by a property the direct opposite of that the possession of which by other substances was the reason for the formation of the class.

To do this may be ingenious; it is certainly not scientific.
Since the time of Lavoisier, since the last decade of the eighteenth century, careful chemists have meant by an element a substance which has not been separated into unlike parts, and they have not meant more than that.

The term _element_ has been used by accurate thinkers as a useful class-mark which connotes a property--the property of not having been decomposed--common to all substances placed in the class, and differentiating them from all other substances.

Whenever chemists have thought of elements as the ultimate kinds of matter with which the physical world is constructed--and they have occasionally so thought and written--they have fallen into quagmires of confusion.
Of course, the elements may, some day, be separated into unlike parts.
The facts of radio-activity certainly suggest some kind of inorganic evolution.

Whether the elements are decomposed is to be determined by experimental inquiry, remembering always that no number of failures to simplify them will justify the assertion that they cannot be simplified.