In many sections of the United States, the productive topsoil is rapidly disappearing.[present tense: the disappearing is ongoing with respect to the present time]
In many sections of the United States, the productive topsoil was
rapidly disappearing. [past tense: the disappearing was ongoing
with respect to a particular point in time]
--James Gilluly, Principles of Geology (modified)
Although astronomers have been accumulating observations of
all the stages in a star's life in recent years, it is fair to say that really tremendous strides have been
taken within the past few years in observing the very earliest stages of stellar life.
[present perfect: the accumulating was ongoing in the past and continues to be ongoing in the
--Martin Cohen, "Star Birth and Maturity"
Do not use the progressive form with states or facts; use the simple present tense or simple past tense instead. Some verbs that commonly describe states are appear, appreciate, be, believe, belong, care, comprise, consider, contain, cost, desire, dislike, doubt, entail, envy, fear, feel, forget, hate, have, hear, imagine, include, know, like, look, love, mean, mind, need, owe, own, possess, prefer, realize, recognize, remember, resemble, see, seem, suppose, taste, think, trust, understand, want, and weigh.
When we compare what we can see of our Galaxy with other galaxies, it is
appearing that our Milky Way Galaxy is resembling a spiral
like many other galaxies, stoked with hundreds of billions of stars unevenly interlaced throughout
chaotic swirls of interstellar gas and dust.
When we compare what we can see of our Galaxy with other galaxies, it appears that our Milky Way Galaxy resembles a spiral like many other galaxies, stoked with hundreds of billions of stars unevenly interlaced throughout chaotic swirls of interstellar gas and dust.
--Eric J. Chaisson, "Our Galaxy"