Core principle: English verb conjugation can be described as the combination of a tense and an aspect.
1The 2 tenses
The 2 grammatical tenses (tenses) ≠ physical time (time).
- The present: ∅ / s
- The preterite: -ED
2The 4 aspects
- The simple aspect: ∅
- The imperfective aspect: BE-ING
- The perfective aspect: HAVE-EN
- The double aspect: HAVE-EN + BE-ING
3The 8 conjugations — tense-aspect combinations
Present (∅ / s)
- The present simple (∅ + ∅/s)
- The present BE-ING (BE-ING + ∅/s)
- The present perfect simple (HAVE-EN + ∅/s)
- The present perfect BE-ING (HAVE-EN + BE-ING + ∅/s)
Preterite (-ED)
- The preterite simple (∅ + -ED)
- The preterite BE-ING (BE-ING + -ED)
- The past perfect simple (HAVE-EN + -ED)
- The past perfect BE-ING (HAVE-EN + BE-ING + -ED)
4A few notes on these markers
- ∅ / s — present marker: the bare verb stem (unchanged), or the -s ending in the 3rd person singular.
- -ED — past marker.
- HAVE-EN — auxiliary have + past participle.
- BE-ING — auxiliary be + verb in -ing (here it really is the -ing ending).
Convention: -ED = preterite and -EN = past participle. This notational distinction tells the two apart; these are not the actual endings.