Question

What do brackets around the first letter of a sentence mean? For a sentence like this;
[T]he dog was said to have been…
What do the brackets here indicate?

Answer 1

Hint: Brackets are markers for "additional details" or material that isn't part of the central content. Brackets are often in pairs, with a "opening" bracket preceding the additional details and a "closing" bracket following it. Brackets are divided into two types: square [] and round ().

Complete answer:
In English, we don't just use square brackets '[]' to communicate extra information; it also serves another reason. When we want to change someone else's terms, we usually use square brackets. Here, we want to emphasize that the change was made by us, and not by the actual composer of that sentence.

In the given question;
Assume that we were given another sentence originally “Rina had heard that the dog was said to have been…”
Now if we wish to re-write only the part that is underlined in that quote, in a way that we place that ‘part’ of the sentence in the beginning, then it would look like;
 [T]he dog was said to have been…

This was done so because the part of the sentence we wished to take, did not begin with a capital letter but with a small letter ‘t’, now to make the sentence grammatically acceptable we needed to convert the ‘t’ to a ‘T’ and this was done by putting ‘T’ in [], so that it doesn’t alter the meaning, rather it indicates to someone else that a change has been made.

Square brackets—[ ]—are used to surround changes in direct quotations whenever authors change or substitute terms. The brackets, which are often used in pairs, enclose terms that are meant to explain context, include a brief description, or assist in the integration of the quote into the reporter's sentence. The use of parentheses instead of brackets is really a common mistake made by authors.

Note: In text, round brackets are used to insert extra details. The text would still be sensible if the brackets and the details inside were removed. Also note that the closing bracket is followed by punctuations like full stop, question mark or exclamation mark (unless a complete text is contained within brackets).