In many sections of the United States, the productive topsoil israpidly disappearing.[present tense: the disappearing is ongoingwith respect to the present time]
In many sections of the United States, the productive topsoil wasrapidly disappearing. [past tense: the disappearing was ongoingwith respect to a particular point in time]
--James Gilluly, Principles of Geology (modified)
Although astronomers have been accumulating observations ofall the stages in a star's life in recent years, it is fair to say that really tremendous strides have beentaken 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 thepresent time]
--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. Someverbs 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, andweigh.
When we compare what we can see of our Galaxy with other galaxies, it isappearing that our Milky Way Galaxy is resembling a spirallike many other galaxies, stoked with hundreds of billions of stars unevenly interlaced throughoutchaotic swirls of interstellar gas and dust.
When we compare what we can see of our Galaxy with other galaxies, itappears that our Milky Way Galaxy resembles aspiral like many other galaxies, stoked with hundreds of billions of stars unevenly interlacedthroughout chaotic swirls of interstellar gas and dust.
--Eric J. Chaisson, "Our Galaxy"
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