Begin with the document class
Standard classes such as article commonly accept 10pt, 11pt or 12pt as a base option, for example \documentclass[12pt]{article}. A journal or thesis class may define different permitted choices.
Follow the actual template’s requirements before adding manual overrides; a class can control headings, captions and other elements separately.
Use named commands within a clear scope
Named commands include \small, \normalsize, \large and \Large; their exact sizes depend on the base size and class. A local group such as {\large A short phrase} limits the change.
For an entire paragraph, keep its paragraph break inside the size scope so the chosen line spacing applies to that paragraph.
Use explicit dimensions deliberately
An explicit selection can use \fontsize{14pt}{18pt}\selectfont: the first value selects the requested size, the second sets the baseline distance. Availability and rendering depend on the font setup.
A larger font without suitable leading can collide with nearby lines. Compare the compiled paragraph, not just a command name.
Separate size from family and mathematics
Changing size does not choose a different family. Read LaTeX typefaces and LaTeX math fonts for those separate jobs. Keep template-defined mathematics and captions consistent with the document.
Your questions, answered.
Are large and Large the same command?
No. LaTeX command names are case-sensitive and these select different named size levels.
Does changing the base size make every template element identical?
No. The class and packages can define their own heading, caption and other styles.
Sources & background
Sources supporting this page’s explanations. Practical examples are our editorial suggestions.