In “The Model Muddle: Proposals for an Immodest Realism”, Marx W. Wartofsky said:
There is an additional trivial truth, which may strike some people as shocking: anything can be a model of anything else!
This implies that between any two things there is at least one property they both share. It reminds me of the “modellability” in Gelbmann (2002), where Gerhard Gelbmann listed six conditions for an object being modellable (signified by “@”)
(1.) the presumed existence of that which is signified by @;
(2.) the givenness of at least one attribute of that which is signified by @;
I think, however, no one would consider that a thing is a model of the other just by them share the same properties – a thing may have many of uses, it is a model if and only if it is used as a model. What kind of the use is “use as model”? the answer is the definition on model-as-use: the use case (I purposely choose this words here) in line with the situation
- The thing (will be a model) have certain property which shares with the other (will be modeled):
– say it is “directly” e.g. the same color;
– say it is “indirectly” e.g. the color is stated in a language (or, encoded).
- The thing works as a substitute of the other:
– can be for any purpose, goal, attempt… even it is no clear.
- The work should be on the properties:
– it is not modeling if working without them;
– the properties takes from the thing are not as itself own but the other.
Then, the thing become a model of the other while the conditions – the situation – is reached. So, we defined
a model is a role in the situation where the role has certain properties of a thing directly or indirectly and works by the properties as a substitute of the thing.
Some things (or people) were born to be a model, so we often call them directly “models”, but we of course know, it is indeed a role (or a job), of the things (or the people).
 Wartofsky, Marx W. (1966). The model muddle: Proposals for an immodest realism. In Cohen, R. S. and Wartofsky, M. W., editors, Models: Representation and the scientific understanding. D. Reidel, Dordrecht, 1979. http://books.google.com.hk/books?id=u7Tfb2eDxOcC
 Gelbmann, Gerhard. (2002). An Outline of Pragmatologic Model-Theory (sec. Stachowiak). Semiotic Subjectivity II. http://sammelpunkt.philo.at:8080/565/
Update on 2012-07-20: add “- the properties takes from …” and the statement of the definition.