Can anyone explain the difference between by contrast and in contrast?
I don't think there is a difference in meaning, only in usage.
This blog post details it:
“In contrast” and “by contrast” mean the same thing: the act of comparing in order to show differences.
The difference lies in the way the words are used.
- “In contrast” is usually followed by “to” or “with” and requires a noun to follow it.
- “By contrast” is usually followed or preceded by the subject of the sentence.
In contrast to the diligent bee, the butterfly flies hither and yon with no apparent purpose.
In contrast with the chorus of birdsongs in my backyard, my front yard is serenaded by the sound of rumbling buses flying down the street.
By contrast, the Picasso is more vibrant and full of life.
The cats will often sleep the day away. The dogs, by contrast, never settle down.
There is no difference in meaning. But usually:
In contrast + to/with + noun
By Contrast + subject of the sentence
Note: According to Longman Dictionary you can use "in contrast" + "(with/to)"
Example For "in contrast":
The stock lost 60 cents a share, in contrast to last year, when it gained 21 cents.
Examples For "by contrast":
The birth rate for older women has declined, but, by contrast, births to teenage mothers have increased.
Both 'in contrast' and 'by contrast' are prepositional expressions. The usage is more versatile for 'in contrast' because it can be more naturally extended to include a substantive followed by 'to', to construct a more complex prepositional phrase with specific content, allowing one to use just one sentence instead of two
(1) "In contrast to bacterial infections diseases, viral infections cannot be treated with antibiotics."
By contrast, 'By contrast' is more used as a simple prepositional expression in the sense of a modifying adverb, typically used to maintain the logical flow at the beginning of sentences:
(2) "Bacterial infections can be treated with antibiotics. By contrast/(In contrast), viral infections do not respond to to this class of drugs".
Note that (2) requires two sentences to say the say the same thing.
In the usage (2) one sees both 'in' and 'by contrast'. However, editors at the leading British scientific journal NATURE, always correct 'in contrast' into 'by contrast' .
As a native English speaker, translator and proof reader, I prefer "in contrast", whereas "by contrast" always jars a little with me (I just came across it in a text I'm revising right now). I can't explain why and I don't know if there is a hard and fast rule (I doubt it), but that's my two cents. When in doubt, leave it out!