Business letters are classified into three types: block, modified block, and semi-block. Each is written in a similar style and contains similar material, however the arrangement changes significantly. Block letters are divided into paragraphs and include many punctuation marks and words used in everyday life. Modified block letters leave out some of the punctuation marks but still indicate divisions between paragraphs by using indentions or margins. Semi-block letters do not have any special design beyond being printed in black ink on white paper.
Block letters are easy to write because you don't need to worry about splitting up sentences or adjusting the position of quotation marks when writing extra words at the end of a sentence. This type of letter is suitable for informal correspondence such as e-mails or social media posts.
Modified block letters are easier to read than block letters because they show where one paragraph ends and the next begins. These letters should be used when writing formal letters because leaving out certain punctuation marks can cause confusion later if you want to add additional information or change something about the letter.
Semi-block letters are best used for documents that need to be printed in black ink on white paper because they look more professional than block letters.
A letter is the most formal form of communication for most commercial reasons. Block letters are divided into paragraphs and include a salutation (a greeting from the writer to the reader) and a closing. Salutations typically include the name of the company or organization along with the person to whom the letter is being sent. Closeings usually include just the sender's signature and address.
Modified block letters are identical to block letters except for one change: there is no division between the body of the letter and the closing. Instead, modifiers such as "Sincerely," "Yours truly," or "Affectionately yours" are included at the end of the letter before the signature and address. Semi-block letters contain some but not all of the elements of a block letter. For example, they may have a salutation but no closing; or perhaps only a modifier at the end.
Letters are commonly used by businesses to communicate with their customers or other companies regarding transactions, issues relating to services or products provided, and so on. Letters can also be used to share congratulations or express sympathy upon hearing sad news. Finally, letters are used when sending notifications about changes to mailing lists, new products/services, etc.
The block format is the most frequent arrangement for a business letter. Except for a double space between paragraphs, the whole letter is left justified and single-spaced in this style. The modified block format is another extensively used format. It is identical to the block format except that each paragraph is given its own indentation level. This format is used when it is important to make a clear separation between parts of the letter.
The tabular format is used to present information in tables. Each column of the table is separated from the other columns by a horizontal rule or some other means of identification. The headings for each column are usually written at the top of the column.
The informal format is used to write an entire letter without using formal styles. This format is commonly used by individuals who are writing one another rather than by businesses sending letters. The main advantage of this format is that it is easy to write a letter in a casual tone as opposed to using formal styles which can come off as stilted and cold.