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From OALD:

sedulous (formal) showing great care and effort in your work
synonym: diligent

assiduous (formal) working very hard and taking great care that everything is done as well as it can be synonym: diligent

diligent (formal) showing care and effort in your work or duties

These definitions look alike. What they have in common is that these words mean to take care and to put effort into your work.

All words are formal. None of these seems to be a proper term in a specific field, e.g. medical, law.

I also looked at Merriam-Webster to get more details. This adds the connotation of steady and earnest to diligent and unremitting attention and persistent application to assiduous. But in the end, these additional information are again describing an equal thing, i.e., continuously doing your work. The entry on sedulous doesn't add any more content; it refers to diligent and again describes the word with perseverance.

From this point (checking dictionaries only), I don't see any difference at all. I continued with a corpora search.

From COCA:

Diligent is most used in combination with work, effort, research, study but also student, people.

She's a diligent student.

His diligent research identified the value of ...

Assiduous is also most used with work, effort, research but not with student, people. Merriam-Webster's Learner's Dictionary entry on assiduous lists student as example though.

He's assiduous in his work.

With assiduous attention to detail ...

Sedulous is most used, um, to little results. BNC has even less content. Merriam-Webster's example is, once again, a student.

So, diligent is used most often, followed by assiduous and sedulous is quite rare.

All words are formal. All words seem to be usable as an attribute to a person (e.g., student) but also specifying the intense care and effort on work, e.g., a research.

I don't see any significant difference in these words, besides frequency. When is a student diligent, assiduous or sedulous? And when is a research diligent, assiduous or sedulous? Or simply: What are the subtle distinctions which aren't represented by dictionaries?

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You might glean something from English synonymes (sic) explained in alphabetical order, but my advice would be to pretend you've never heard of sedulous (I hadn't until now, and it's never done me any harm! :) For the other two, use diligent when you want to emphasise how dutifully someone carries out some precise instructions, and assiduous to emphasise how precisely someone performs their duties. –  FumbleFingers Dec 18 '12 at 23:36

4 Answers 4

up vote 12 down vote accepted

There is no difference in core meaning, and even the connotational penumbrae overlap a lot. It's mostly about the attitude you're trying to convey; and this is going to depend more on each reader's actual experience with the words than with any broad consensus.

Here's how I would use them:

  • Diligent if I wanted to express respect and admiration for the worker's application to her project
  • Assiduous if I wanted to express respect for the worker's application and thoroughness, while leaving room to doubt the value of her work
  • Sedulous if I wanted to acknowledge the worker's application and thoroughness, while leaving room to wonder whether the work might not be better served by insight and imagination

But that's a very personal view; others may feel differently.

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I don't really have an opinion on sedulous (apart from the possibility that using it might mark you out as a lexical show-off). But I think my personal opinion on the other two is probably very similar to yours. To me, diligent people are usually those who reliably follow instructions to the letter; assiduous people are very thorough and exacting, even if they're just doing something of their own choosing. –  FumbleFingers Dec 18 '12 at 23:42
@FumbleFingers I think all three may be used of 'self-starters' - though in that case I suppose one is "instructed" by the needs of the job rather than a supervisor. But as I said, it all depends on who you've been listening to and reading. They're very close. –  StoneyB Dec 21 '12 at 16:41
I like that - as per usual - you make your key point straight away (no difference in core meaning). I assumed that by leaving room to doubt the value... you were implying that an assiduous person might just devote meticulously thorough attention to detail in anything they happen to be doing (not necessarily even "goal-oriented" from others' point of view). Whereas express respect and admiration implies the diligent person does exactly and thoroughly whatever they're supposed to do (i.e. some assigned task, their job/duty). –  FumbleFingers Dec 21 '12 at 17:47
I agree that to me "diligent" has connotations of following instructions exactly, carrying out assigned duties to the fullest, or meeting every specified requirement (see: "due diligence"). Whereas "assiduous" on the other hand doesn't have those connotations, even though it has the same meaning. And I've never even heard the word "sedulous" before. –  Ben Lee Dec 21 '12 at 19:14

Of the three synonyms, diligent is by far the most commonly used, in my experience. And sedulous is the least common — you'll get a lot of strange looks if you use it.

I use and hear diligent much more often than assiduous.

Assiduous is more about attentiveness/attention/attendance, and diligence is more about effort.

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That's interesting. I think of diligent as more formulaic than assiduous; that is to say, a diligent person follows instructions to the letter, while an assiduous person puts great energy and effort into everything she does. I recently used "assiduity" over "diligence" in a letter of recommendation because I wanted to emphasize the student's earnest and unremitting application, as opposed to just an ability to sit there and finish his work. To me personally, assiduous is the word that leaves less room to doubt the value of the work, while diligent seems more mechanical.

My mental analogy is as follows:

Assiduous : Practicing writing skills :: Diligent : Reciting times tables

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Sedulous sounds like studious. I use sedulous in regards to people who live a lifestyle that in the real world is in alignment with being like a professional athlete. A Mike Jordan if you will.

Jordan practices basketball diligently as well as goes over the pre and post game tapes with assiduous detail, but over all as a person who not only watches what he eats but pain stakenly rises early, is never poorly dressed and has millions of products solid to his name, all we can say is that he is a sedulous being of profound wisdom and vigor.

PS. Diligent is over used and I found sedulous by seeking the hard to find antomyms for indolent, yet my seaking was diligent and attention to detail assiduous.

Pps. Using vocabulary to mind manipulate others into feeling less than is not my goal by avoiding the diligent word, rather seeking fresh ways to edify powerful people taking rare actions of transformative quality.

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