The reason we say “grammatically” instead of “grammarically” lies in the distinction between the parts of speech and their respective forms in English.

Understanding the Terms

• Grammar: This is a noun that refers to the system and structure of a language, including rules that govern the composition of phrases and sentences.

• Grammatical: This is an adjective derived from the noun “grammar.” It describes something that conforms to the rules of grammar. For example, one might say, “This sentence is grammatical,” meaning it follows the accepted grammatical rules.

• Grammatically: This is an adverb formed from the adjective “grammatical.” It is used to describe actions or states in relation to grammar. For instance, “This sentence is grammatically correct” means that the sentence adheres to grammatical rules.

Etymology and Usage

The suffix “-ly” is commonly used in English to form adverbs from adjectives. In contrast, “grammarically” would suggest a direct formation from “grammar,” which is not standard in English usage. The established forms are:

• Adjective: Grammatical
• Adverb: Grammatically

Using “grammarically” would not only be incorrect but also unconventional, as it does not follow the typical morphological patterns of English word formation. Thus, “grammatically” is preferred for clarity and correctness when discussing adherence to grammatical rules.

References

1. HiNative - Grammatical vs. Grammatically Correct
2. The Free Dictionary Forum - Grammatical vs. Grammatically Correct
3. Cambridge Dictionary - Grammatical
4. Reddit - Grammar - Is It a Grammar Error or a Grammatical Error?
5. Merriam-Webster - Grammatical
6. Merriam-Webster - Is “Grammatical Error” a Contradiction?
7. Leitner Studios - The History of Pareidolia and How to Use It
8. Pure - Pareidolia in Advertising