We need not, to be sure, expect to find such ideas in every piece of literature. An idea, of the sort that we have in mind, although of necessity readily available to imagination, is more general in connotation than most poetic or literary images, especially those appearing in lyric poems that seek to capture a moment of personal experience. Thus Burns's ``My love is like a red, red rose'' and Hopkins' ``The thunder-purple sea beach, plumed purple of thunder'' although clearly intelligible in content, hardly present ideas of the sort with which we are here concerned. On the other hand, Arnold's ``The unplumbed, salt, estranging sea,'' taken in its context, certainly does so.

Understanding a work of art involves recognition of the ideas that it reflects or embodies. Thus the student of literature may sometimes find it helpful to classify a poem or an essay as being in idea or in ideal content or subject matter typical or atypical of its period. Again, he may discover embodied within its texture a theme or idea that has been presented elsewhere and at other times in various ways. Our understanding will very probably require both these commentaries. Very likely it will also include a recognition that the work we are reading reflects or ``belongs to'' some way of thought labelled as a ``school'' or an ``-- ism,'' i. e. a complex or ``syndrome'' of ideas occurring together with sufficient prominence to warrant identification. Thus ideas like ``grace,'' ``salvation,'' and ``providence'' cluster together in traditional Christianity. Usually the work studied offers us a special or even an individualized rendering or treatment of the ideas in question, so that the student finds it necessary to distinguish carefully between the several expressions of an ``-- ism'' or mode of thought. Accordingly we may speak of the Platonism peculiar to Shelley's poems or the type of Stoicism present in Henley's ``Invictus,'' and we may find that describing such Platonism or such Stoicism and contrasting each with other expressions of the same attitude or mode of thought is a difficult and challenging enterprise. After all, Shelley is no ``orthodox'' or Hellenic Platonist, and even his ``romantic'' Platonism can be distinguished from that of his contemporaries. Again, Henley's attitude of defiance which colors his ideal of self mastery is far from characteristic of a Stoic thinker like Marcus Aurelius, whose gentle acquiescence is almost Christian, comparable to the patience expressed in Milton's sonnet on his own blindness.