diff --git a/concepts/arrays/about.md b/concepts/arrays/about.md
index 62704a4a..56ff22eb 100644
--- a/concepts/arrays/about.md
+++ b/concepts/arrays/about.md
@@ -1,6 +1,7 @@
 # About
 
-Arrays are Factor's fixed-length, immutable sequence type.
+Arrays are Factor's fixed-length sequence type: you can change the
+elements but not the length.
 Literals use `{ … }` with whitespace between elements; the
 `arrays` vocabulary adds small constructors that pull values off
 the stack:
diff --git a/concepts/arrays/introduction.md b/concepts/arrays/introduction.md
index caca76f3..9c43ec76 100644
--- a/concepts/arrays/introduction.md
+++ b/concepts/arrays/introduction.md
@@ -1,7 +1,8 @@
 # Introduction
 
-Arrays are Factor's primary fixed-length, immutable sequence
-type, written `{ … }`. The `arrays` and `sequences` vocabularies
+Arrays are Factor's primary fixed-length sequence type, written
+`{ … }`: you can change the elements but not the length. The `arrays`
+and `sequences` vocabularies
 together give you small constructors that take values off the
 stack, plus everyday operations for joining, reversing, and
 looking up elements.
diff --git a/concepts/sequences/about.md b/concepts/sequences/about.md
index 895673f8..205739e4 100644
--- a/concepts/sequences/about.md
+++ b/concepts/sequences/about.md
@@ -42,10 +42,10 @@ with the others.
 | `find-last` | `( seq quot -- i/f elt/f )`       |
 | `produce`   | `( pred quot -- seq )`            |
 
-Arrays are immutable; the `prefix`/`suffix`/`append`/`prepend` operations all
-return new sequences without modifying the original. Vectors are
-mutable — `push` and `pop` work in place — but `clone` is the right
-starting point if you want a fresh copy.
+Arrays are fixed-length, so the `prefix`/`suffix`/`append`/`prepend`
+operations all return new sequences rather than growing the original.
+Vectors are resizable — `push` and `pop` work in place — but `clone`
+is the right starting point if you want a fresh copy.
 
 ## Conversions
 
diff --git a/exercises/concept/boatswains-bilge/.docs/introduction.md b/exercises/concept/boatswains-bilge/.docs/introduction.md
index 735a65f7..3a71f83b 100644
--- a/exercises/concept/boatswains-bilge/.docs/introduction.md
+++ b/exercises/concept/boatswains-bilge/.docs/introduction.md
@@ -1,10 +1,10 @@
 # Introduction
 
-Pumps, valves, hoses — anything that holds an OS handle has to
-be *released* when you're done with it. Factor's
-[`destructors`][destructors] vocab wraps these in a framework
-that guarantees cleanup, even when an exception unwinds the
-stack midway through a routine.
+Pumps, valves, hoses — anything that holds an operating-system
+resource (an open file, a network connection) has to be *released*
+when you're done with it. Factor's [`destructors`][destructors] vocab
+wraps these in a framework that guarantees cleanup, even when an error
+interrupts your code partway through.
 
 ## The class and the generic
 
diff --git a/exercises/concept/cargo-shuffle/.docs/introduction.md b/exercises/concept/cargo-shuffle/.docs/introduction.md
index 05b6fe4c..fd5da871 100644
--- a/exercises/concept/cargo-shuffle/.docs/introduction.md
+++ b/exercises/concept/cargo-shuffle/.docs/introduction.md
@@ -1,9 +1,10 @@
 # Introduction
 
 Welcome to Factor! Factor is a *concatenative* language: instead of
-calling functions with parenthesised arguments, you write a sequence of
-**words** that pass values to each other through a shared **data
-stack**. Picture a stack of cargo crates on a quay, newest on top.
+calling functions like `square(add(2, 3))`, you write a row of
+**words** left to right — `2 3 + square` — that pass values to each
+other through a shared **data stack**. Picture a stack of cargo crates
+on a quay, newest on top.
 
 ## Comments
 
diff --git a/exercises/concept/currency-conversion/.docs/introduction.md b/exercises/concept/currency-conversion/.docs/introduction.md
index 6d959f13..8a91ebef 100644
--- a/exercises/concept/currency-conversion/.docs/introduction.md
+++ b/exercises/concept/currency-conversion/.docs/introduction.md
@@ -15,8 +15,8 @@ float in one calculation, the result comes out as a float:
 2 3.0 + .    ! => 5.0
 ```
 
-Underscores are allowed inside number literals as digit separators
-and are ignored by the parser.
+You can put underscores inside a number to group the digits —
+`1_000_000` — and Factor just ignores them.
 
 ## Division words
 
diff --git a/exercises/concept/dragons-descendants/.docs/introduction.md b/exercises/concept/dragons-descendants/.docs/introduction.md
index 50064b2a..954c0c02 100644
--- a/exercises/concept/dragons-descendants/.docs/introduction.md
+++ b/exercises/concept/dragons-descendants/.docs/introduction.md
@@ -3,7 +3,8 @@
 Tuples can extend other tuples. `TUPLE: child < parent slots ;`
 declares a class whose instances are also instances of `parent`
 — they get the parent's slots in addition to their own, and the
-parent's accessors work on them transparently.
+parent's accessors work on them too, just as if they'd been defined on
+the child.
 
 ```factor
 USING: accessors ;
diff --git a/exercises/concept/factory-failsafe/.docs/introduction.md b/exercises/concept/factory-failsafe/.docs/introduction.md
index 7f6cda81..c6756ea5 100644
--- a/exercises/concept/factory-failsafe/.docs/introduction.md
+++ b/exercises/concept/factory-failsafe/.docs/introduction.md
@@ -1,8 +1,8 @@
 # Introduction
 
 Factor's error system has three pieces: `throw` to signal an error,
-`recover` to handle one, and `ERROR:` to define a tuple-typed error
-class.
+`recover` to handle one, and `ERROR:` to define your own kind of
+error.
 
 ## `throw`
 
diff --git a/exercises/concept/lasagna/.docs/introduction.md b/exercises/concept/lasagna/.docs/introduction.md
index 2f61f5b0..6de7f634 100644
--- a/exercises/concept/lasagna/.docs/introduction.md
+++ b/exercises/concept/lasagna/.docs/introduction.md
@@ -25,7 +25,8 @@ values from the top of the stack and pushes some values back.
 ```
 
 A related word, `.s`, prints the *whole* data stack without consuming
-anything — handy at the listener for seeing what a snippet leaves
+anything — handy in the listener (Factor's interactive prompt, where
+you type code and see results) for seeing what a snippet leaves
 behind. It's why later examples sometimes end in `.s` rather than `.`:
 they leave more than one value on the stack, and `.s` shows them all.
 
diff --git a/exercises/concept/librarians-ledger/.docs/introduction.md b/exercises/concept/librarians-ledger/.docs/introduction.md
index afe54bc6..813798da 100644
--- a/exercises/concept/librarians-ledger/.docs/introduction.md
+++ b/exercises/concept/librarians-ledger/.docs/introduction.md
@@ -13,10 +13,10 @@ for the running form.
 reduce ( seq init quot: ( prev elt -- next ) -- result )
 ```
 
-`reduce` walks a sequence, threading an accumulator through a
-two-argument quotation. The quotation receives the running
-accumulator and the next element; whatever it leaves on the
-stack becomes the new accumulator.
+`reduce` goes through a sequence one item at a time, carrying along a
+running result (the *accumulator*) and feeding it to a two-argument
+quotation. The quotation receives the running accumulator and the next
+element; whatever it leaves on the stack becomes the new accumulator.
 
 ```factor
 USING: math sequences ;
diff --git a/exercises/concept/mixed-juices/.docs/introduction.md b/exercises/concept/mixed-juices/.docs/introduction.md
index da0c02fe..8433f484 100644
--- a/exercises/concept/mixed-juices/.docs/introduction.md
+++ b/exercises/concept/mixed-juices/.docs/introduction.md
@@ -15,7 +15,8 @@ until ( pred body -- )
 
 `pred` and `body` are both quotations that operate on the data
 stack. `while` keeps looping while `pred` leaves a truthy value;
-`until` is the symmetric form (loop while `pred` leaves `f`).
+`until` is the opposite: it keeps looping *until* `pred` becomes true
+(that is, while `pred` leaves `f`).
 
 A single piece of state can flow on the stack between the
 predicate and the body:
diff --git a/exercises/concept/mosaic-making/.docs/introduction.md b/exercises/concept/mosaic-making/.docs/introduction.md
index b554c24b..e49917ff 100644
--- a/exercises/concept/mosaic-making/.docs/introduction.md
+++ b/exercises/concept/mosaic-making/.docs/introduction.md
@@ -1,10 +1,10 @@
 # Introduction
 
-Arrays are Factor's fixed-length, immutable sequence type. You
-already know how to write a literal array — `{ … }` — and how to
-slice and aggregate one. This exercise covers the small toolkit
-that comes up when you build arrays from values on the stack and
-then look up or rearrange their contents.
+Arrays are Factor's fixed-length sequences: you can change the
+elements, but not the length. You already know how to write a literal
+array — `{ … }` — and how to slice and aggregate one. This exercise
+covers the small toolkit that comes up when you build arrays from
+values on the stack and then look up or rearrange their contents.
 
 ## Building from the stack
 
diff --git a/exercises/concept/quayside-crew/.docs/introduction.md b/exercises/concept/quayside-crew/.docs/introduction.md
index bd47b974..ef321fd1 100644
--- a/exercises/concept/quayside-crew/.docs/introduction.md
+++ b/exercises/concept/quayside-crew/.docs/introduction.md
@@ -3,7 +3,7 @@
 Factor's threads are *cooperative coroutines* — they share one OS
 thread, hand control to each other at I/O and at explicit yield
 points, and never run truly simultaneously. Anything you do
-*between* yields is effectively atomic. But if a compound
+*between* yields happens as one uninterrupted step. But if a compound
 operation (read-modify-write) yields midway, another thread can
 slip in and change the world before you finish — and that's a race.
 
diff --git a/exercises/concept/role-playing-game/.docs/introduction.md b/exercises/concept/role-playing-game/.docs/introduction.md
index d4544ffd..0e0a1df0 100644
--- a/exercises/concept/role-playing-game/.docs/introduction.md
+++ b/exercises/concept/role-playing-game/.docs/introduction.md
@@ -1,6 +1,7 @@
 # Introduction
 
-A *tuple* is Factor's record/struct/class type. Each tuple class has
+A *tuple* bundles several named values together into one object — what
+other languages call a record, struct, or class. Each tuple class has
 a fixed set of named slots and Factor automatically generates getters
 and setters for them.
 
diff --git a/exercises/concept/rpn-calculator/.docs/introduction.md b/exercises/concept/rpn-calculator/.docs/introduction.md
index 17ec24e2..d6dac844 100644
--- a/exercises/concept/rpn-calculator/.docs/introduction.md
+++ b/exercises/concept/rpn-calculator/.docs/introduction.md
@@ -1,8 +1,8 @@
 # Introduction
 
-A *quotation* — code in `[ ]` brackets — is a first-class value in
-Factor. You can store one in a variable, put one in an array, pass
-one to another word, and *call* it later.
+A *quotation* — code in `[ ]` brackets — is itself a value in Factor,
+just like a number or a string. You can store one in a variable, put
+one in an array, pass one to another word, and *call* it later.
 
 ## `call`
 
diff --git a/exercises/concept/signalers-satchel/.docs/introduction.md b/exercises/concept/signalers-satchel/.docs/introduction.md
index 69eb8984..0b495355 100644
--- a/exercises/concept/signalers-satchel/.docs/introduction.md
+++ b/exercises/concept/signalers-satchel/.docs/introduction.md
@@ -59,7 +59,7 @@ string can coerce with `>string`.
 ## `?head` and `?tail` — strip a marker if present
 
 Framed readings carry marker text that may or may not be there.
-`?head` and `?tail` (in `sequences`) try to strip a prefix or
+`?head` and `?tail` (in `splitting`) try to strip a prefix or
 suffix, returning the (possibly shortened) sequence *and* a
 boolean reporting whether the marker was found: