I want to know the number of inflectional forms of a verb.
I came to know from one of my colleagues that a verb has 13 inflectional forms ('conjugations,' that's what he named it). Is it true?
It depends on what you include as 'inflectional'. If you mean compound tenses then I suppose you could get close to that number. Let's try:
I eat, I am eating, I was eating, I ate, I have eaten, I had eaten, I will eat, I will have eaten, I could eat, I could have eaten, I would eat, I would have eaten, to eat (infinitive).
Well that's 13 but I can think of others e.g. having eaten, having been eating, was eaten etc.
There are also the different person endings such as he eats, thou eatest, etc, as well as the person differences in the compound tenses with 'were' replacing 'was' and 'has' replacing 'have' in some of them.
No doubt someone will think of more.
Latinate intransitive verb: cogitate
Germanic transitive/intransitive verb: light
Old English common verb: go
Old English irregular verb: be
My descriptions here only serve to indicate the origin and relative age of the examples. The oldest verbs have the most inflected forms, in many cases (like went) because they have picked up parts of other verbs which are now at best archaic if not obsolete (wend).
Many of these forms are used with auxiliary verbs which may themselves be inflected. I am discounting those; as WS2 notes in his answer, calling those an “inflected form” yields more than thirteen anyway.
However, even if I have missed a few in each case, to get to thirteen will be very difficult and I would be interested in how your colleague identified that many.