"нежели" vs. "чем"

Question

I have always been taught, and have used, the word "чем" when making comparisons (or the genitive case sometimes). However, I have recently encountered the word "нежели" several times in books, used just like "чем". For example:

"Этот мир оказался притягательнее, нежели тот, в котором мы к тому времени прожили..."

Is this rather bookish/formal? Should I attempt to incorporate it into my speech, or will it sound strange in most situations? Does it have subtleties that differentiate it from "чем"?

Answer 1

"Нежели" is bookish, but it is not archaic. I use it in everyday speech quite often, and dictionaries do not mark it as obsolete.

According to Большой Толковый Словарь, it can be used in all the same contexts as "чем". However, I can notice some differences that are not described in the dictionary.

1) I prefer to use "чем" instead of "нежели" to introduce a comparison which is expressed as a sentence:

Горы были выше, чем я предполагал. (I will not use "нежели" here, it sounds odd)
Горы были выше, чем на Кавказе. (I can use "нежели" here, it will sound natural)

2) You can use "нежели" with adjectives in analytic form, i.e. forms with "более\менее". "чем" doesn't work with analytic forms:

Время от времени вырождение, снижение активности и продуктивности более удобны, нежели эволюция

But:

Время от времени вырождение, снижение активности и продуктивности удобнее, чем эволюция

Answer 2

Not only "нежели" is more bookish, like @YellowSky had already mentioned, but is is also cannot be used in all contexts, even when "high-style" speech is appropriate.

For example, you can not say: "Нежели дурью маяться, сходил бы погулял" (this will sound very unnatural even in "bookish" speech) but only "Чем дурью маяться, сходил бы погулял".

Though in past, indeed, those were 100% interchangeable. But nowadays forms like "нежели чем" instead of "прежде чем" are completely out of usage.

Also, it worth to mention a common mistake of modern native speakers - the usage of redundantly complex form "нежели чем" ("Для мужчин рак груди более опасен нежели, чем для женщин"). In most cases it's nothing more than an overkill :)