Learn English – What’s the difference between “hence” and “thus”

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.

Examples:

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.

I don't remember how I learned this, and I can't find a reference just now, but the peculiar custom of redundancy in our legal documents dates back to medieval England. The Norman conquest of 1066 put a French-speaking king and nobility in charge of an English-speaking people. The English courts at the time were extremely sensitive to detail and would throw out a petition for something as minor as a misspelling, so getting every detail right was crucial. Thus, lawyers developed a habit of incorporating English synonyms for key French words (or it might have been the reverse; memory fails me on that detail). This is how we get phrases like null and void and cease and desist. Since American law (except in the state of Louisiana) is based on English common law, the U.S. inherited this custom. Over time, I suspect the legal professional largely forgot exactly why it was building all this redundancy into its documents and "decided" it was as a general matter of belt-and-suspenders caution.

EDIT: I finally found a reference of sorts at Wikipedia:

David Crystal (2004) explains a stylistic influence upon English legal language. During the Medieval period lawyers used a mixture of Latin, French and English. To avoid ambiguity lawyers often offered pairs of words from different languages. Sometimes there was little ambiguity to resolve and the pairs merely gave greater emphasis, becoming a stylistic habit. This is a feature of legal style that continues to the present day. Examples of mixed language doublets are: "breaking and entering" (English/French), "fit and proper" (English/French), "lands and tenements" (English/French), "will and testament" (English/Latin). Examples of English-only doublets are: "let and hindrance", "have and hold."