What do you mean singular? I span, you span, he/she/it span, we span, you span, they span. These all sound grammatical to me. I can’t think of many English verb

What do you mean singular? I span, you span, he/she/it span, we span, you span, they span. These all sound grammatical to me. I can’t think of many English verbs that inflect differently for the same person but different number. In fact off the top of my head the only one I can think of is “to be” (I am, we were)