形态学是语言学的一个分支（也是语法的主要组成部分之一），它研究单词结构，尤其是语素，语素是语言的最小单位。它们可以是基础词或构成词的成分，如词缀。形容词的形式是形态的。

随时间变化的形态

传统上，词法与句法有着基本的区别，前者主要关注单词的内部结构，后者主要关注单词在句子中的组合方式。

"The term 'morphology' has been taken over from biology where it is used to denote the study of the forms of plants and animals ... It was first used for linguistic purposes in 1859 by the German linguist August Schleicher (Salmon 2000), to refer to the study of the form of words," noted Geert E. Booij, in "An Introduction to Linguistic Morphology." (3rd ed., Oxford University Press, 2012)

然而，近几十年来，许多语言学家对这种区分提出了质疑。例如，词汇语法和词汇功能语法（LFG），它考虑了词汇和语法之间的相互关系，甚至相互依存。

形态学的分支和方法

形态学的两个分支包括对单词的分解（分析方面）和重组（合成方面）的研究；也就是说，屈折变化形态学关注的是将单词分成不同的部分，例如后缀如何构成不同的动词形式。​相比之下，词汇构词法涉及到新基础词的构建，尤其是来自多个语素的复杂基础词。词汇构词法又称词汇形态学和派生形态学。

作者David Crystal给出了以下示例：

"For English, [morphology] means devising ways of describing the properties of such disparate items as a, horse, took, indescribable, washing machine, and antidisestablishmentarianism. A widely recognized approach divides the field into two domains: lexical or derivational morphology studies the way in which new items of vocabulary can be built up out of combinations of elements (as in the case of in-describ-able); inflectional morphology studies the ways words vary in their form in order to express a grammatical contrast (as in the case of horses, where the ending marks plurality)." ("The Cambridge Encyclopedia of the English Language," 2nd ed. Cambridge University Press, 2003)

作者Mark Aronoff和Kirsten Fuderman也以这种方式讨论并举例说明了两种方法：

"The analytic approach has to do with breaking words down, and it is usually associated with American structuralist linguistics of the first half of the twentieth century....No matter what language we're looking at, we need analytic methods that are independent of the structures we are examining; preconceived notions might interfere with an objective, scientific analysis. This is especially true when dealing with unfamiliar languages. "The second approach to morphology is more often associated with theory than with methodology, perhaps unfairly. This is the synthetic approach. It basically says, 'I have a lot of little pieces here. How do I put them together?' This question presupposes that you already know what the pieces are. Analysis must in some way precede synthesis." (Mark Aronoff and Kirsten Fudeman, "What Is Morphology?" 2nd ed. Wiley-Blackwell, 2011)