diff --git a/DESCRIPTION b/DESCRIPTION
index 9f47b08b..6b28a199 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -34,6 +34,7 @@ Imports:
     ggplot2 (>= 3.4.0),
     ggridges (>= 0.5.5),
     glue,
+    lifecycle,
     posterior,
     reshape2,
     rlang (>= 0.3.0),
diff --git a/NAMESPACE b/NAMESPACE
index b8cf818b..56bfb045 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -226,3 +226,6 @@ importFrom(dplyr,top_n)
 importFrom(dplyr,ungroup)
 importFrom(dplyr,vars)
 importFrom(ggplot2,"%+replace%")
+importFrom(lifecycle,deprecate_warn)
+importFrom(lifecycle,deprecated)
+importFrom(lifecycle,is_present)
diff --git a/R/bayesplot-helpers.R b/R/bayesplot-helpers.R
index d3d86ec3..f5467946 100644
--- a/R/bayesplot-helpers.R
+++ b/R/bayesplot-helpers.R
@@ -446,19 +446,28 @@ plot_bg <- function(on = TRUE, ...) {
 
 #' @rdname bayesplot-helpers
 #' @export
-#' @param color,size Passed to [ggplot2::element_line()].
-#'
-grid_lines <- function(color = "gray50", size = 0.2) {
+#' @param color,linewidth Passed to [ggplot2::element_line()].
+#' @param size `r lifecycle::badge("deprecated")` Use `linewidth` instead.
+#'
+grid_lines <- function(color = "gray50", linewidth = 0.2, size = deprecated()) {
+  if (lifecycle::is_present(size)) {
+    lifecycle::deprecate_warn(
+      "1.16.0",
+      "grid_lines(size)",
+      "grid_lines(linewidth)"
+    )
+    linewidth <- size
+  }
   theme(
-    panel.grid.major = element_line(color = color, linewidth = size),
-    panel.grid.minor = element_line(color = color, linewidth = size * 0.5)
+    panel.grid.major = element_line(color = color, linewidth = linewidth),
+    panel.grid.minor = element_line(color = color, linewidth = linewidth * 0.5)
   )
 }
 
-grid_lines_y <- function(color = "gray50", size = 0.2) {
+grid_lines_y <- function(color = "gray50", linewidth = 0.2) {
   theme(
-    panel.grid.major.y = element_line(color = color, linewidth = size),
-    panel.grid.minor.y = element_line(color = color, linewidth = size * 0.5)
+    panel.grid.major.y = element_line(color = color, linewidth = linewidth),
+    panel.grid.minor.y = element_line(color = color, linewidth = linewidth * 0.5)
   )
 }
 
diff --git a/R/bayesplot-package.R b/R/bayesplot-package.R
index 2727a62a..db740a9a 100644
--- a/R/bayesplot-package.R
+++ b/R/bayesplot-package.R
@@ -5,6 +5,7 @@
 #'
 #' @import ggplot2 stats rlang
 #' @importFrom dplyr %>% summarise group_by select
+#' @importFrom lifecycle deprecated deprecate_warn is_present
 #'
 #' @description
 #' \if{html}{
diff --git a/R/helpers-gg.R b/R/helpers-gg.R
index 953a51d4..21ec794a 100644
--- a/R/helpers-gg.R
+++ b/R/helpers-gg.R
@@ -24,17 +24,10 @@ geom_ignore <- function(...) {
 
 #' Add new aesthetic mappings to a list of aesthetic mappings
 #'
-#' @param mapping a list of `uneval` aesthetic mappings (created by `aes_()`)
-#' @param ... additional mappings to add, e.g., `color = ~ parameter`
+#' @param mapping a list of `uneval` aesthetic mappings (created by `aes()`)
+#' @param ... additional mappings to add using `.data$` syntax
 #' @return the updated list
 #' @noRd
-modify_aes_ <- function(mapping, ...) {
-  utils::modifyList(mapping, aes_(...))
-}
-
-#' Same as `modify_aes_` but using `aes()` instead of `aes_()` (now deprecated).
-#' Often `...` will need to contain expression of the form `.data$x` to avoid R cmd check warnings
-#' @noRd
 modify_aes <- function(mapping, ...) {
   utils::modifyList(mapping, aes(...))
 }
diff --git a/R/mcmc-diagnostics.R b/R/mcmc-diagnostics.R
index 2727928f..f363026d 100644
--- a/R/mcmc-diagnostics.R
+++ b/R/mcmc-diagnostics.R
@@ -77,7 +77,7 @@
 #' (p <- mcmc_acf_bar(x, pars = c("alpha", "beta[1]")))
 #'
 #' # add horiztonal dashed line at 0.5
-#' p + hline_at(0.5, linetype = 2, size = 0.15, color = "gray")
+#' p + hline_at(0.5, linetype = 2, linewidth = 0.15, color = "gray")
 #' }
 #'
 #' # fake rhat values to use for demonstration
diff --git a/R/mcmc-scatterplots.R b/R/mcmc-scatterplots.R
index 4d32391c..d4f939e1 100644
--- a/R/mcmc-scatterplots.R
+++ b/R/mcmc-scatterplots.R
@@ -109,7 +109,7 @@
 #' color_scheme_set("pink")
 #' (p3 <- mcmc_scatter(x, pars = c("alpha", "beta[3]"), alpha = 0.25, size = 3))
 #' p3 + geom_smooth(method = "lm", se = FALSE, color = "gray20",
-#'                  size = .75, linetype = 2)
+#'                  linewidth = .75, linetype = 2)
 #'
 #' \donttest{
 #' if (requireNamespace("hexbin", quietly = TRUE)) {
diff --git a/man/MCMC-diagnostics.Rd b/man/MCMC-diagnostics.Rd
index 35e589dc..f6dbad81 100644
--- a/man/MCMC-diagnostics.Rd
+++ b/man/MCMC-diagnostics.Rd
@@ -163,7 +163,7 @@ color_scheme_set("pink")
 (p <- mcmc_acf_bar(x, pars = c("alpha", "beta[1]")))
 
 # add horiztonal dashed line at 0.5
-p + hline_at(0.5, linetype = 2, size = 0.15, color = "gray")
+p + hline_at(0.5, linetype = 2, linewidth = 0.15, color = "gray")
 }
 
 # fake rhat values to use for demonstration
diff --git a/man/MCMC-scatterplots.Rd b/man/MCMC-scatterplots.Rd
index e82f0797..8799e2a0 100644
--- a/man/MCMC-scatterplots.Rd
+++ b/man/MCMC-scatterplots.Rd
@@ -313,7 +313,7 @@ p2 + stat_density_2d(color = "black", size = .5)
 color_scheme_set("pink")
 (p3 <- mcmc_scatter(x, pars = c("alpha", "beta[3]"), alpha = 0.25, size = 3))
 p3 + geom_smooth(method = "lm", se = FALSE, color = "gray20",
-                 size = .75, linetype = 2)
+                 linewidth = .75, linetype = 2)
 
 \donttest{
 if (requireNamespace("hexbin", quietly = TRUE)) {
diff --git a/man/bayesplot-helpers.Rd b/man/bayesplot-helpers.Rd
index 897bce92..460511d0 100644
--- a/man/bayesplot-helpers.Rd
+++ b/man/bayesplot-helpers.Rd
@@ -63,7 +63,7 @@ panel_bg(on = TRUE, ...)
 
 plot_bg(on = TRUE, ...)
 
-grid_lines(color = "gray50", size = 0.2)
+grid_lines(color = "gray50", linewidth = 0.2, size = deprecated())
 
 overlay_function(...)
 }
@@ -112,7 +112,9 @@ example, facet text can be removed by adding \code{facet_text(on=FALSE)}, or
 simply \code{facet_text(FALSE)} to a ggplot object. If \code{on=TRUE} (the default),
 then \code{...} can be used to customize the appearance of the theme element.}
 
-\item{color, size}{Passed to \code{\link[ggplot2:element]{ggplot2::element_line()}}.}
+\item{color, linewidth}{Passed to \code{\link[ggplot2:element]{ggplot2::element_line()}}.}
+
+\item{size}{\ifelse{html}{\href{https://lifecycle.r-lib.org/articles/stages.html#deprecated}{\figure{lifecycle-deprecated.svg}{options: alt='[Deprecated]'}}}{\strong{[Deprecated]}} Use \code{linewidth} instead.}
 }
 \value{
 A \strong{ggplot2} layer or \code{\link[ggplot2:theme]{ggplot2::theme()}} object that can be
diff --git a/tests/testthat/test-convenience-functions.R b/tests/testthat/test-convenience-functions.R
index 7b197f27..a6f76499 100644
--- a/tests/testthat/test-convenience-functions.R
+++ b/tests/testthat/test-convenience-functions.R
@@ -63,7 +63,7 @@ test_that("lbub works", {
 
 # plot and facet backgrounds ----------------------------------------------
 test_that("grid_lines returns correct theme object", {
-  thm <- theme_default() + grid_lines(size = 1.5, color = "purple")
+  thm <- theme_default() + grid_lines(linewidth = 1.5, color = "purple")
   expect_equal(thm$panel.grid.major, element_line(linewidth = 1.5, color = "purple"))
   expect_equal(thm$panel.grid.minor, element_line(linewidth = 0.75, color = "purple"))
 })