What's the past tense of 'underlie'?

Today, democratic principles underlie our system of  government. In the past, different principles did the same for older systems of government.

How would you put that in the past tense?

In the past, principles underlied older systems of government?




When the question popped into my head recently, I had to confess I had no idea. I know that the past tense of lie is lay. But underlie is its own word. And the standard way past tenses are formed is by adding ed or, sometimes after changing a y to an i. So if the verb underlie is regular, its past tense would be underlied. As in, Different principles underlied older systems of government.

But that just doesn’t sound right. And when we tinker with different forms, most would agree that underlay sounds best of all. “In the past, different principles underlay those systems of government.”

Mark this as exhibit ZZZZ in the case to prove that the ear usually guesses right.

Here’s what Webster’s New World College Dictionary says:

underlie. transitive verb underlay, underlain, underlying

to lie under or beneath: trusses underlie the roof

  1. to
    be the basis for; form the foundation of
  2. Finance
    to have priority over (another) in order of claim, as a bond

Dictionaries have a system for telling you the past forms of verbs. After the main entry, they list the past tense and past participle in bold, in that order.

So open the dictionary to the word blow and you’ll see right next to it blew then blown. That’s how you know how it’s: Today the winds blow. Yesterday they blew. In the past they have blown.

But if you look up walk in most dictionaries, you’ll see no such forms after the main entry. That's because most dictionaries include past forms only for irregular verbs. Regular verbs get their past forms the same way: by adding ed for both the simple past tense and the past participle. And they explain this stuff right up front in the section on how to use the dictionary. So when a verb has no past tense or past participle after its main dictionary entry, you know it's a regular verb that uses "ed" for both. Today they walk. Yesterday they walked. In the past they have walked.

So, based on the dictionary entry for underlie, we know it’s: Today these principles underlie government. Not long ago, other principles underlay government. In the past, many different principles have underlain government.

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