In the following sentence, is the word "obtain" a bare infinitive (an infinitive without "to")?

My parents insisted that he obtain his bachelor's degree.

No. It would be a use of the subjunctive. This is detectable, in modern English, in the third-person singular of the Present Tense, where the subjunctive lacks the -s ending: "It is necessary that he see a doctor." In your sentence, it is 'he obtain' rather than 'he obtains'.

In the sentence:
"My parents have said that he must obtain his bachelor's degree before we get married."

Here, it would be modal + bare infinitive:: must + obtain

My parents insisted that he obtain his bachelor's degree.


Yes, it is a bare infinitival, being used to form a subjunctive clause.

"Subjunctive" is a type of clause construction headed by a plain (infinitival) verb-form.


PaulM