{
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  "body": "\n## Summary\n\nWhen the [[implication|0ZNX6DQ3EJ]] $p \\to q$ is true, $p$ is a sufficient condition for $q$, and $q$ is a necessary condition for $p$.\nA condition $p$ is necessary and sufficient for $q$ when $p \\to q$ and $q \\to p$ are both true, that is, when $p \\leftrightarrow q$ is true.\n\n## Remarks\n\n\"$p$ only if $q$\" means $p \\to q$, and \"$p$ if $q$\" means $q \\to p$.\n\"Necessary and sufficient\" is another way to say \"if and only if\". See [[biconditional|0V6GAWTBYW]].\nFor an integer $n$, \"$n$ is divisible by $4$\" is sufficient but not necessary for \"$n$ is even\".\n\n## Explanations\n\n### L1 human\n\nA sufficient condition is enough to get the result.\nA necessary condition is one that you cannot do without.\nTo have a driving licence is necessary to drive legally, but it is not sufficient: you also need a car.\n",
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