I saw words like desirable, desired, preferable, preferred,…. As I checked some example sentences they are almost synonyms:
it is desirable to check that nothing has been forgotten
it is desired to check that nothing has been forgotten
the user can select a desired element
the user can select a desirable element
What is their difference?
Best Answer
Though the words are often interchangeable, there is a subtle difference that can sometimes make for different meanings. The suffix able truly does mean "able to be" or "capable of." It may not actually happen, but it is at least hypothetically possible. The past participle, however, means that you know that it is actually the case, or actually happened.
I think this difference is most pronounced in verbs that are negated, for example with the un- prefix. Consider unbreakable vs. unbroken. "The walls are unbreakable" means it's not even theoretically possible to break them. Whereas "The walls are unbroken" means that they have not yet broken, but it's still possible they might break it the future.
Still, there is a lot of overlap between the meanings. In your examples, both versions of the word make sense based solely on their definitions. So how to decide which sounds more natural and idiomatic?
I think the best way to make this judgement is based on specificity. Words ending in able sound more abstract -- they're often used when you're describing a quality inherent to the subject, something that a lot of people would agree on. The past participle, however, is specific.
So, to say that something is desirable means that it has qualities that you think would make a lot of people want it. There's generally a lot of agreement about what things are desirable. When you say something is desired, you are saying that it would make a particular person want it. Desired properties are more personal; what one person desires could be quite different from what another person desires.
For the first example,
sounds better. You're suggesting that this is not so much a personal opinion, but that lots of people would agree with you on this.
In the second example,
sounds better. In this case, you're talking about an element that a specific person (the user) desires. Different users would likely desire different elements for different purposes, so it's unlikely that there would be any consensus on what a "desirable" element would be.
(As an aside: "it is desirable" and similar constructs sound overly-formal and somewhat unnatural. A better way to rephrase the first example is something like, "you should always check that nothing has been forgotten").