diff --git a/src/commands.rs b/src/commands.rs
index 9d400cb..c0db926 100644
--- a/src/commands.rs
+++ b/src/commands.rs
@@ -1,15 +1,31 @@
+use std::{collections::HashMap, sync::Mutex};
+
 use rand::seq::SliceRandom;
 
 /// this is where we keep data for the bot
-/// we can probably eventually serialize this to disk for cheap persistence
+// can we eventually serialize this to disk for cheap persistence?
 #[derive(Default)]
-pub struct Data {}
+pub struct Data {
+    facts: Mutex<HashMap<String, String>>,
+}
 type Error = Box<dyn std::error::Error + Send + Sync>;
 type Context<'a> = poise::Context<'a, Data, Error>;
 
 /// all of the commands supported by `buscemi`
 pub fn commands() -> Vec<poise::Command<Data, Error>> {
-    vec![ping(), eight_ball()]
+    vec![help(), ping(), eight_ball(), know()]
+}
+
+/// print helpful information
+#[poise::command(prefix_command, slash_command)]
+async fn help(
+    ctx: Context<'_>,
+    #[description = "optional command to show help about"]
+    #[autocomplete = "poise::builtins::autocomplete_command"]
+    command: Option<String>,
+) -> Result<(), Error> {
+    poise::builtins::help(ctx, command.as_deref(), Default::default()).await?;
+    Ok(())
 }
 
 /// check that the bot is working
@@ -62,3 +78,45 @@ async fn eight_ball(
     ctx.say(answer).await?;
     Ok(())
 }
+
+/// remember some important knowledge
+///
+/// usage:
+/// ```
+/// @buscemi (remember|know) [that] <OBJECT> [is] <DEFINITION>
+/// ```
+/// examples:
+/// ```
+/// @buscemi remember that x is y
+/// @buscemi know foo is bar
+/// ```
+/// technically works but confusing:
+/// ```
+/// @buscemi remember 1 2
+/// ```
+#[poise::command(prefix_command, slash_command, aliases("remember"))]
+async fn know(
+    ctx: Context<'_>,
+    #[description = "the thing you want to define"] that: String,
+    #[rest]
+    #[description = "the definition of the thing"]
+    is: String,
+) -> Result<(), Error> {
+    let (that, is) = if that.as_str() == "that" {
+        is.split_once(' ').unwrap()
+    } else {
+        (that.as_str(), is.as_str())
+    };
+    let is = is.strip_prefix("is ").unwrap_or(is);
+    let old = {
+        let mut facts = ctx.data().facts.lock().unwrap();
+        facts.insert(that.to_string(), is.to_string())
+    };
+    let message = if let Some(old) = old {
+        format!("ok, {that} is {is} (changed from {old})")
+    } else {
+        format!("ok, {that} is {is}")
+    };
+    ctx.say(message).await?;
+    Ok(())
+}