The problem
Has this ever happened to you? You're editing a document in Microsoft Word, and all of a sudden, instead of inserting the new text you're typing, with every keystroke you're deleting and replacing your existing text! Here's how it might look:
Imagine your Word document contains the following sentence:
This is my |interesting text.
You then place your text cursor (the vertical blinking line or "insertion point") right before the word "interesting" and type "wonderful" Your intention is to insert this word. Normally, you'd get this:
This is my wonderful|interesting text.
However, in this crazy-making situation, you get this instead:
This is my wonderful|ng text.
The 9-character word "wonderful" has replaced the first 9 characters of "interesting," leaving you with "wonderfulng" which is probably not what you wanted.
The explanation: Insert mode (good) vs. Overtype mode (bad)
If you are experiencing this odd behavior in Microsoft Word, this means that you have accidentally switched from "Insert mode" (the default) to "Overtype mode." Word's help system describes Overtype as a mode where you "replace existing characters as you type."
Overtyping (also known as overstrike or typeover) made sense decades ago when all text was monospaced, i.e., every character you typed had the same width. For example, you could construct a crude table using spaces to perfectly line up the columns, and later you might use Overtype mode to "type over" parts of that table to update it without inserting or shifting any text to the right.
Modern computers and word processors typically use proportional-spaced fonts, where narrow letters use less space than wider ones. Here's the difference:
Monospaced font Courier, different letters all have the same width:
Proportional-spaced font Verdana, different letters have different widths
(However, even in proportional-spaced fonts, the digit characters 0-9 are usually monospaced so that tables of figures line up properly.)
Here are ways you can turn off Overtype mode:
Quick fix #1 in Microsoft Word for Windows (any version): Tap the "insert" key on the keyboard
How it can happen: If you have a full-size Windows keyboard, tapping the "Insert" key once toggles between Insert mode and Overtype mode.
How to fix it: If you find yourself in Overtype mode, just tap the Insert key on your keyboard once more, and you'll probably be back in Insert mode. Type a few characters at the start of an existing paragraph to be sure.
If you have a Windows laptop and you can't find an "insert" key, look for the "INS" key. Depending on your keyboard, you may also have to hold down a "modifier" key (like "FN" or "Mode") first.
Quick fix #2 in Microsoft Word (Windows or Macintosh, any version): Close and reopen
First, you may want to use the Undo command (if available) to restore your text to what it was before you started overtyping. You'll probably have to invoke the Undo command multiple times, once for each keystroke.
Then, close all Word documents (saving your changes as appropriate), close the Word program itself, then reopen your document. (If you're not sure whether you've closed Word, you could certainly Restart your computer.) That will get you out of Overtype mode and back to Insert mode.
Quick fix #3 in Microsoft Word for Windows (any version): Turn off the "Overtype mode" option
To turn Overtype mode off, you open Word's Options, look for "Edit" or "Advanced Editing" (the details will depend on which version of Word you have), and then uncheck the "Overtype mode" option.
