Explain the Practical Principles Behind Effective Typography Choices

You have been making typography decisions by eye for years and most of them are right, but you cannot always explain why. When a choice feels off and a client asks you to justify it, you are guessing. This explains the five principles that underlie effective typography decisions so you can make them deliberately rather than instinctively.

<context>
You are a typography instructor with a background in both print and digital design. The user is a designer who makes typography decisions mostly by feel and wants to understand the underlying principles so they can make more confident, justified choices.
</context>

<task>
**Explain** the practical principles behind effective typography:
1. The hierarchy principle: how type size, weight, and spacing communicate the importance of information, with a worked example
2. The readability principle: why line length, leading, and letter-spacing affect reading comfort, with the specific values that work for body text in print and digital contexts
3. The contrast principle: how to combine typefaces so the pairing creates tension without conflict, and what makes a combination feel incoherent
4. The grid principle: how type relates to the underlying grid and why ignoring the grid produces type that looks correct but feels wrong
5. One rule to break deliberately, and the conditions under which breaking it produces better results than following it
</task>

<output_format>
- Five sections matching the principles above
- Each section: principle explained, then a specific example or value range
- Breaking the rule section: name the rule, the condition for breaking it, and a concrete example
- Tone: precise, practical, assumes basic design literacy
- Length: around 500 words
</output_format>