I was wondering if I could use the term "by and large" in the first sentence of my introduction. For example somthing like this: By and large, it is established beyond doubt that...
According to Merriam-Webster online,
Definition of by and large : on the whole : in general
Examples of by and large in a sentence: By and large, that information is accurate.
Did You Know? By and large is originally a sailing term meaning "alternately close-hauled and not close-hauled." A ship that is sailing "close-hauled" is sailing as directly into the wind as possible (typically within about 45 degrees of the wind). The "by" part of the phrase means "close-hauled." (This "by" also appears in the term full and by, meaning "sailing with all sails full and close to the wind as possible.") "Large," by contrast, refers to a point of sail in which the wind is hitting the boat "abaft the beam," or behind the boat's widest point. A 1669 example of a variant spelling of "by and large" gives us a sense of the range implied: "Thus you see the ship handled in fair weather and foul, by and learge" (S. Sturmy, Mariners Magazine). The suggestion of a wide range carries over into the term's "in general" sense.
First Known Use of by and large 1706
To my ear, starting your essay with this phrase, although correct, weakens rather than strengthens your premise. "By and large" means, generally. Also, the phrase is an idiom and colloquial, fine for conversation, but not appropriate for an essay.
This somewhat weak phrase "by and large" precedes the more strongly worded "it is established beyond doubt that..." and undercuts its strength.
"By and large" means "on the whole" but implies mostly, but not universally.
How can a proposition be both beyond doubt, and not universally accepted?
By saying "it is established beyond doubt," you have already implied general acceptance of whatever proposition you are going to introduce.