: Ensure you have the version of Forge compatible with 1.4.6 (avoid "latest" versions if they are meant for newer Minecraft updates).
To install Thaumcraft 3 for Minecraft 1.4.6, you must use the legacy Thaumcraft 3 Wiki Installation Guide : mainkraft 1 4 6 skachat mod taumkraft
: Get the Thaumcraft 3 ZIP/JAR file. Sources like the Minecraft Forum often host archives for older versions. : Ensure you have the version of Forge compatible with 1