Authors can attempt to persuade their audience through using comparisons. In creative writing such as poetry and fiction, it is legitimate to compare two items that seem at first to be dissimilar in order to produce a literary effect such as surprise, humour or an unexpected perspective. In creative writing, it may be permissible to say 'it was raining Wellington boots', or 'the moon is a goddess riding her chariot of clouds'. Literary critics have to decide whether such comparisons work to create the desired effect on the audience. Valid comparisons
For most types of critical thinking, comparisons must be valid, and add to our understanding of the situation. In scientific terms, for example, it doesn't help to think of the moon as a goddess or clouds as chariots. Comparisons draw attention to those aspects which are similar. As two things are never identical, it takes critical evaluation and judgement to decide whether a comparison is valid for the context. If the comparison helps to give a more accurate understanding, then it is likely to be valid. Example
The heart works as a pump, moving blood through the body by opening and constricting. For most purposes, the comparison with a pump helps us to understand the action of the heart, so this is valid. An analogy is not valid if:
* the two items being compared are not sufficiently similar, or. . . * the comparison is misleading, or . . .
* the item used for comparison is described inaccurately. Before reading on, check whether you can identify the weaknesses in the analogy in the example below. Example
Cloning of human cells should never be allowed: it will create another Frankenstein. We do not want such monsters.
The author's position on cloning is clear: that it is wrong and should be stopped. It may be that the idea of cloning is 'monstrous' to many people and the author is playing on that sentiment. However, the analogy used is not valid as it doesn't compare like...