meta- + pherein = ana- + logos ?

I was asked recently if I knew what the difference between metaphor and analogy is. My first thought: "Of course!" My second: "Wait. No."

Thankfully, the great Google knows all. It took me to my old friends dictionary.com and etymonline.com and had them explain things to me in ways I can understand. (The great Google is too powerful to spend time explaining things to me.)

The first thing I learned is a fun fact. Did you know [met-a-fawr] can be pronounced [met-a-fer]? What is that? British? Who cares, I like it!

Anyway, according to dry definition, the difference between metaphor and analogy is the difference between

"a figure of speech in which a term or phrase is applied to something to which it is not literally applicable in order to suggest a resemblance; something used [...] to represent something else"

and

"agreement or similarity, especially in a certain limited number of features or details; a comparison made to show such similarity."

It's easy to see how these concepts might get conflated. Both involve the comparison between two entities that aren't obviously related. Hopefully etymology will shed some light on this question that seems in a certain limited number of details like a shadow...

Metaphor began in its Greek infancy as meta- "over, across" (or "after," "along with," "beyond," "among," "behind" -- it's a broad prefix) plus pherein "to carry, bear." (The suffix -phore indicates "a person or thing that bears or produces".) Metapherein was a verb synonymous with transfer, carry over, change, and alter and was from its inception applied to words used in a strange way. In the 1500s it appeared in the English language with connotations bizarrely intact.

Analogy, on the other hand, began as a strictly mathematical term, which Plato picked up and began using more broadly. Today it is still used as a formal term in logical mathematics to mean "a form of reasoning in which a similarity between two or more things is inferred from a known similarity between them in other respects." Analogy came from the Greek word analogia, "proportion," itself born of the marriage between the roots ana- "upon, according to" and logos "ratio" or "word, speech, reckoning". 

Analogy appeared in English within several decades of its cousin metaphor. The fine distinction between them has been preserved through Greek, Latin, French, and English cultures for millennia, suggesting we might be the first people to question whether there is a useful difference between them! And we may decide that there is none, but it's worth first finding out what we are leaving behind when we confuse them.

To all my practical readers who want to know, "So can you just tell me when to use one or the other or not?" -- If you analyze objects with mathematical precision in one of the many realms of science ("The sky reminds me in a particular way of the hues of a Chiquita banana sitting beside a deep orange mango."), you're probably smart and probably using an analogy. If you do the same thing without thinking too hard about it, you're likely creating a metaphor ("Check that tropical smoothie sunset!" "Dude, you're weird.").