"Consistence" and "consistency"

What is the relation and difference between the nouns consistence and consistency?

For example, which one should be used in the following sentence?

Although he has passed the exam, he is suggested to take the next one, because they would like to test his consistence/consistency.

According to the OED, both consistence and consistency are valid nouns. Consistence originally had many meanings, which include:

• Standing or remaining still, quiescence; state of rest. Obs.
• Continuance, endurance; continuing state
• A settled condition of affairs. Obs.
• concr. Matter dense enough to cohere. Obs. or poet.
• The degree of firmness with which the particles of a substance cohere; degree of density. (Usually of more or less viscous liquids.)
• consistency

As you can see, many of its definitions (of which there are 8 listed) are now obsolete. The last recorded use of consistence to mean consistency was in 1878. Consistency has now taken over many of these meanings, and is used far more often than consistence. Using consistence would not be incorrect, but it is an archaic form of a word that many people would not recognize today.

Unless you want to be a couple of centuries out of date, use consistency, like everyone else.

Consistence isn't a word anymore. It died. Use consistency.

One property of concrete is described in accordance with Eurocodes (BS EN 1992-1-1:2004) in terms of consistence. Under previous British Stadards the word workability was used. Consistence is measured by tests such as the slump test which indicate the way in which the material holds together and flows under its own weight. It is a technical term and in no way incorrect or obsolete.