Though "certes" is no longer commonly used in everyday conversation, it can still appear in classic literature and legal contexts where a more formal or emphatic tone is appropriate. It remains a part of the lexicon of older English texts, particularly those from the 14th to the 17th century.
The decline in usage is part of a broader trend in the simplification of language over time. Many expressions and words that were once widely used in the Middle Ages have been replaced with more contemporary terms. Despite this, "certes" is still occasionally used by those seeking a dramatic or archaic style in their writing or speech.
Understanding words like "certes" provides a window into the evolution of the English language and its rich history of borrowing from other languages such as Latin and Old French. It is a reminder of the varied expressions of certainty that have existed throughout time.